Fan and water heater provided with the same, and impeller and water heater provided with the same

ABSTRACT

A fan includes: an impeller including a main plate having a first plane, a plurality of first blades each formed the first plane, and a shroud formed integrally with the plurality of first blades; a fan case; a drive source; and a rotation shaft. The first blades each include a linearly protruding region that is linearly increased in height from an outer circumferential side to an inner circumferential side, and a curvedly protruding region that is curvedly increased in height from the outer circumferential side to the inner circumferential side, the height extending in a direction in which each first blade protrudes. The linearly protruding region is welded to the main plate. Accordingly, a highly durable fan can be implemented that allows sufficient durability to be maintained even under a high temperature environment or an acid environment.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a fan and a water heater provided withthe fan, and an impeller and a water heater provided with the impeller.

Description of the Background Art

In replacement of an already placed tank water heater with aninstantaneous water heater, there are locations where an already placedexhaust pipe (a B vent) cannot be removed from a point of view ofmaintaining appearance of buildings.

At such a location, a water heater can be replaced by leaving thealready placed exhaust pipe and inserting an exhaust tube (a flexibleexhaust tube) in the exhaust pipe. The exhaust tube should be smaller indiameter, because the exhaust tube cannot be placed in the exhaust pipeif the exhaust tube has a large outer diameter. In order to maintain astable combustion state even when the exhaust tube is decreased indiameter, an exhaust suction and combustion type should be adopted for awater heater.

A water heater of this exhaust suction and combustion type is disclosed,for example, in Japanese Patent Laying-Open No. 60-186617. In the waterheater described in this publication, a heat exchanger for recoveringsensible heat, a heat exchanger for recovering latent heat, and a fanare arranged in this order on a downstream side in a flow of acombustion gas produced in a burner. Namely, in the water heater of thistype, the fan is arranged downstream of the heat exchanger in the flowof the combustion gas, and the fan suctions combustion gas having passedthrough the heat exchanger and emits the combustion gas to the outsideof the water heater.

In addition, an impeller having a plurality of blades around therotation shaft is known as a component of the fan (for example, JapanesePatent Laying-Open No. 2000-356197, Japanese Patent Laying-Open No.2010-242543, Japanese Patent Laying-Open No. 2010-281256, U.S. publishedpatent application No. 2008/0279682 (specification), and JapaneseUtility Model Laying-Open No. 04-040191). This impeller is driven by amotor or the like and rotated, thereby achieving the air-blowingfunction of the fan.

Such an impeller is formed of a plurality of components. There is aknown method for producing the impeller by ultrasonic-welding resincomponents such as a blade to each other for assembly.

Ultrasonic welding is a processing technique for instantaneously meltingand joining a thermoplastic resin by minute ultrasonic vibration andwelding pressure. According to the ultrasonic welding, a portion weldedby ultrasonic waves is generally made of a material that is once meltedand thus becomes brittle. Consequently, this portion may often be lowerin durability and strength than the base material. Furthermore, whenwelding is insufficient, durability and strength may be further lowered.

Therefore, when an impeller is produced by means of welding such asultrasonic welding, sufficient welding of the weld portion is requiredin order to maintain the durability and strength of the impeller.

Furthermore, it is also conceivable to use a resin containing a fibrousfiller in order to increase the strength of the impeller. However, ithas been found that, in the case where a resin containing a fibrousfiller is used to produce a resin component including a disc-shaped (orannular) main plate and a plurality of blades each extending in theradial direction of the main plate, a distortion occurs in the shape ofthe resin component, particularly in the shape of the main plate in theradial direction, with the result that the flatness of the main platetends to decrease.

When a resin component having a main plate with decreased flatness isultrasonic-welded to another component, these components cannot beequally pressurized, so that ultrasonic vibration cannot be stablytransmitted. Consequently, welding of these components tends to beinsufficient. Furthermore, when a distortion occurs in the shape of themain plate of the impeller, the motion balance performance of theimpeller may be decreased, so that the air-blowing performance may bedecreased.

Particularly, the impeller of the fan used for a water heater of anexhaust suction and combustion type is placed within a passage ofcombustion gas, and therefore, exposed to a higher temperatureenvironment as compared with the conventional case. Furthermore, theimpeller of the fan used for a water heater of a latent heat recoverytype adapted to an exhaust suction and combustion system is exposed alsoto strong-acid drainage water produced by recovery of latent heat, inaddition to a high-temperature environment. In such a case, it isstrongly required to sufficiently weld each component to particularlymaintain the durability of the impeller.

SUMMARY OF THE INVENTION

The present invention has been made in light of the above-describedproblems. An object of the present invention is to provide a highlydurable fan that allows sufficient durability to be maintained evenunder a high temperature environment or an acid environment, and a waterheater provided with the fan.

Furthermore, another object of the present invention is to provide animpeller that is excellent in durability and strength and capable ofexhibiting stable air-blowing performance, and a water heater providedwith the impeller.

A fan of the present invention includes: an impeller including a mainplate formed in a disc shape and having a first plane, a plurality offirst blades each formed so as to extend from an inner circumferentialside to an outer circumferential side of the first plane of the mainplate and protrude from the first plane, and a shroud covering theplurality of first blades and formed integrally with the plurality offirst blades; a fan case housing the impeller; a drive source attachedto the fan case for driving the impeller; and a rotation shaft couplingthe impeller and the drive source. The first blades each include: alinearly protruding region that is linearly increased in height from theouter circumferential side to the inner circumferential side; and acurvedly protruding region that is curvedly increased in height from theouter circumferential side to the inner circumferential side, the heightextending in a direction in which each first blade protrudes from thefirst plane. The curvedly protruding region is located closer to theinner circumferential side of the first plane than the linearlyprotruding region is. The linearly protruding region is welded to themain plate.

In the fan of the present invention, the shroud has an outercircumferential portion having a shape that is linearly inclined in theradial direction of the main plate so as to correspond to the shape ofthe linearly protruding region of each first blade. Accordingly, a jigof an ultrasonic welding machine is pressed against this outercircumferential portion (the linearly inclined region), therebyimproving adhesiveness between the jig and the shroud, so thatultrasonic vibration can be stably transmitted to a weld portion.Thereby, the main plate and each first blade can be sufficiently welded.Therefore, the fan of the present invention has excellent durability.

In the above-described fan, the curvedly protruding region is defined asa non-weld region that is not welded to the main plate.

When the curvedly protruding region is to be welded to the main plate,it is necessary to press the jig of the ultrasonic welding machineagainst the curvedly inclined region of the shroud (a portioncorresponding to the curvedly protruding region of the first blade) fortransmitting ultrasonic vibration. However, ultrasonic vibration cannotbe sufficiently transmitted to a curved surface, thereby leading toinsufficient welding or causing welding strength variations, which arenot preferable for a product. Therefore, by not welding the curvedlyprotruding region to the main plate, it becomes possible to produce animpeller having stable quality but not undergoing variations in strengthof welding between the main plate and the first blade. Consequently, thequality of the fan can be stabilized.

In the above-described fan, the impeller further includes a plurality ofsecond blades each formed so as to extend from an inner circumferentialside to an outer circumferential side of the second plane of the mainplate on a side opposite to the first plane and protrude from the secondplane. When the main plate is seen from an axial direction of therotation shaft, each second blade is located between two first bladesadjacent to each other.

Accordingly, at the time of ultrasonic welding, the weld portion of themain plate is supported at its plane from the second plane side (theplane on the second blade side) by a welding jig, so that the main plateis stably held. Consequently, ultrasonic vibration is readilysufficiently transmitted to the weld portion. Therefore, the main plateand the first blade can be sufficiently welded.

In the above-described fan, when the main plate is seen from an axialdirection of the rotation shaft, a portion including an outercircumferential end of each of the first blades is disposed in a radialdirection of the main plate.

This allows airflow to smoothly flow in the direction along thecentrifugal force, which is caused by rotation of the impeller, in theouter circumferential portion onto which the centrifugal force isgreatly exerted. Consequently, the weld portion is less likely to comeoff.

In the above-described fan, when the main plate is seen from the axialdirection of the rotation shaft, a portion including an outercircumferential end of each of the second blades is disposed in a radialdirection of the main plate.

Accordingly, when the main plate is seen from the axial direction of therotation shaft, each second blade can be readily disposed so as to belocated between two first blades adjacent to each other.

In the above-described fan, a plurality of positioning concave portionsare provided in the first plane of the main plate, and the plurality offirst blades are inserted into and welded to the plurality ofpositioning concave portions, respectively.

Accordingly, positional misalignment at the time of welding between themain plate and each first blade can be prevented, so that the weldingstrength can be improved.

In the above-described fan, a positioning protrusion is formed at an endof the curvedly protruding region of the first blade on a side oppositeto the shroud, and the protrusion is fitted in a hole provided in thefirst plane of the main plate.

Accordingly, positional misalignment of the curvedly protruding region(non-weld region) of the first blade can be prevented.

A water heater of the present invention is a water heater of a latentheat recovery type capable of heating water by recovering latent heat ofcombustion gas, and includes: a burner generating combustion gas; a heatexchanger heating water flowing through inside by heat exchange withcombustion gas; and a fan suctioning combustion gas having passedthrough the heat exchanger and emitting combustion gas to outside of thewater heater. The above-described fan is attached such that a side onwhich the shroud is provided is located on a side close to the burner.

Consequently, when the shroud and each first blade are integrally formedto weld the main plate and each first blade (formed integrally with theshroud), the weld portion with low durability is located on theunderside of the main plate (on the burner side). Accordingly, the weldportion is less likely to be exposed to drainage water, so that the weldportion can be protected from corrosion caused by drainage water.Therefore, it becomes possible to provide a water heater including ahighly durable fan that can withstand a high-temperature environment.

An impeller of the present invention includes a main plate, a pluralityof first blades, a shroud, and a plurality of second blades. The mainplate formed in a disc shape has a first plane and a second plane on aside opposite to the first plane. The first blades each are welded tothe first plane of the main plate so as to extend from an innercircumferential side to an outer circumferential side of the first planeand protrude from the first plane. The shroud serves to cover theplurality of first blades. The second blades each are formed so as toextend from an inner circumferential side to an outer circumferentialside of the second plane and protrude from the second plane. The mainplate and the plurality of second blades are integrally molded by aresin containing a fibrous filler. The second blades each have at leastone of a configuration in which each second blade extends so as to crossa radial direction of the main plate and a configuration in which eachsecond blade is separated by a slit into an inner blade member locatedon the inner circumferential side and an outer blade member located onthe outer circumferential side.

The present inventors have carried out concentrated studies toconsequently find that, when the main plate and the second blades areintegrally molded by a resin containing a fibrous filler, the secondblades act to resist shrinkage of the main plate, thereby causing adistortion to occur in the main plate.

Specifically, the present inventors have found as follows: in anintegrally molded product including a main plate and second blades andintegrally molded by a resin containing a fibrous filler, the fillertends to spread relatively randomly in the disc-shaped main plate,whereas the filler tends to be oriented in each second blade in itsextending direction. Accordingly, if each second blade extends along astraight line in the radial direction of the main plate, the filleroriented in the second blade acts as large resistance against radialshrinkage of the resin, thereby causing a difference in shrinkage amountof the main plate in the radial direction of the main plate between theregion where a second blade is formed and the region where a secondblade is not formed. This causes uneven shrinkage of the resin in theradial direction at the time when the main plate is molded, with theresult that the flatness of the main plate is decreased.

In contrast, in the case where the second blade is configured to extendso as to cross the radial direction of the main plate, it becomespossible to reduce resistance by the filler oriented in the second bladeagainst radial shrinkage of the resin. The same also applies to the casewhere the second blade is configured to be separated by a slit into aninner blade member located on the inner circumferential side and anouter blade member located on the outer circumferential side.

Therefore, according to the impeller of the present invention, itbecomes possible to suppress uneven shrinkage of the main plate in theradial direction caused by existence of the second blade. Accordingly,the flatness of the main plate can be improved, so that the integrallymolded product including the main plate and the second blade can besufficiently welded to another component. Therefore, excellentdurability and strength can be achieved while stable air-blowingperformance can be exhibited.

According to the above-described impeller, at least a part of eachsecond blade is formed in a curved line in plan view as seen from adirection orthogonal to the second plane of the main plate.

Accordingly, it becomes possible to reduce resistance caused by thefiller oriented in the second blade against radial shrinkage of theresin, so that the flatness of the main plate can be more improved.

According to the above-described impeller, each second blade has anS-shape in plan view as seen from a direction orthogonal to the secondplane of the main plate.

Accordingly, it becomes possible to reduce the resistance caused by thefiller oriented in the second blade against radial shrinkage of theresin, so that the flatness of the main plate can be further improved.

In the above-described impeller, the second blade is configured to beseparated by the slit into the inner blade member located on the innercircumferential side and the outer blade member located on the outercircumferential side, and a third blade extending from the innercircumferential side to the outer circumferential side of the secondplane is provided between the outer blade members adjacent to eachother.

Accordingly, the air-blowing capability on the second plane side of theimpeller can be improved.

In the above-described impeller, a positioning protrusion is provided atan end of each first blade on a side opposite to the shroud, apositioning hole is provided in the second plane of the main platebetween the second blades adjacent to each other, and the protrusion isfitted in the hole.

Accordingly, positional misalignment at the time of welding between themain plate and the first blade can be prevented, so that weldingstrength can be increased.

In the above-described impeller, a boss portion protruding from thefirst plane is provided in a center portion of the main plate, and abearing hole penetrating from the first plane toward the second plane isprovided in a center portion of the boss portion. The boss portion isformed so as to be continuously increased in size from an end portion ofthe boss portion toward the first plane, and a thinned portion isprovided in the boss portion on the second plane side.

Accordingly, the strength of the boss portion can be increased while adistortion of the boss portion can be suppressed.

A water heater of the present invention includes: a burner generatingcombustion gas; a heat exchanger heating water flowing through inside byheat exchange with combustion gas; and a fan suctioning combustion gashaving passed through the heat exchanger and emitting combustion gas tooutside of the water heater. The fan includes a fan case, an impellerhoused within the fan case, a drive source attached outside the fancase, and a rotation shaft coupling the impeller and the drive source.The fan case has a back surface wall provided with a through hole. Theimpeller is arranged so as to have the second plane facing the backsurface wall. A gap through which air outside the fan case is suctionedinto the fan case is provided between the rotation shaft penetrating thethrough hole and the back surface wall. The impeller included in thiswater heater is the impeller as described above.

According to the water heater of the present invention, the air-blowingcapability of the fan can be achieved by the air-blowing force on thefirst plane side of the impeller while the drive source can be cooledand backflow of combustion gas can be prevented by the air-blowing forceon the second plane side of the impeller. Furthermore, since theimpeller is excellent in durability and strength and can exhibit stableair-blowing performance, excellent fan performance can be achieved.

An impeller of the present invention includes a first member and asecond member. The first member includes a shroud formed in an annularshape and a first blade that is formed so as to extend from an innercircumferential side to an outer circumferential side of a first backsurface of the shroud and protrude from the first back surface. Thesecond member includes a main plate formed in a disc shape and a secondblade that is formed so as to extend from an inner circumferential sideto an outer circumferential side of a second back surface of the mainplate and protrude from the second back surface. The first member andthe second member are integrally molded by a resin containing a fibrousfiller. The first member and the second member are coupled by weldingthe first blade and a second front surface on a side opposite to thesecond back surface. Furthermore, at least one of the second frontsurface and a first front surface on a side opposite to the first backsurface includes an inner circumferential side gate mark portion locatedon a circumference on the inner circumferential side and an outercircumferential side gate mark portion located on a circumference closeto the outer circumferential side relative to the inner circumferentialside gate mark portion.

The present inventors have found that the uniformity of the shape of theshroud (main plate) is decreased when the first member (second member)made of a resin containing a fibrous filler is molded using a moldingdie including: a first space (corresponding to the shroud or the mainplate) having an area extending in the circumferential direction; and asecond space (corresponding to the first blade or the second blade)provided in a slit shape so as to protrude from this first space, andalso including: a gate provided in the first space on the innercircumferential side. The present inventors have also found as follows:the filler tends to spread relatively randomly in the first space,whereas the filler tends to be oriented in the second space in itsextending direction, in which case the filler oriented in the secondspace acts to resist shrinkage of the resin in the first space.Accordingly, the shrinkage amount of the resin in the radial directionof the shroud and the main plate is different between the region wherethe first and second blades are formed and the region where the firstand second blades are not formed. This causes uneven shrinkage of theresin in the radial direction at the time when the shroud and the mainplate are molded, with the result that the uniformity of the shape ofeach of the shroud and the main plate is deteriorated.

In contrast, when a resin is injected not only from the innercircumferential side gate located on the circumference on the innercircumferential side in the first space but also from the outercircumferential side gate located on the circumference close to theouter circumferential side relative to the inner circumferential sidegate, the flow of the resin moving from the outer circumferential sidein the first space of the molding die through the outer circumferentialside gate exerts an influence upon the flow of the resin moving from theinner circumferential side to the outer circumferential side in thefirst space of the molding die through the inner circumferential sidegate. This causes a disturbance in the flow of the resin from the innercircumferential side gate. Accordingly, as compared with the case wherea resin is injected only from the inner circumferential side gate,orientation of the filler in the second space can be suppressed, so thatresistance caused by the orientation of the filler can be reduced.

In the second member, the second front surface of the main plate has aninner circumferential side gate mark portion located on thecircumference on the inner circumferential side and an outercircumferential side gate mark portion located on the circumferenceclose to the outer circumferential side relative to the innercircumferential side gate mark portion. This second member is molded byinjecting a resin from the inner circumferential side gate located onthe circumference on the inner circumferential side in the space for amain plate and also from the outer circumferential side gate located onthe circumference close to the outer circumferential side relative tothe inner circumferential side gate. Therefore, in the second memberhaving such a gate mark, uneven shrinkage of the main plate in theradial direction caused by existence of the second blade can besuppressed for the reason as described above. Consequently, theuniformity of the shape of the main plate can be improved, therebyallowing sufficient welding between the first member and the secondmember that includes the main plate and the second blade. Accordingly,excellent durability and strength can be achieved while stableair-blowing performance can be exhibited.

On the other hand, in the first member, the first front surface of theshroud has an inner circumferential side gate mark portion located onthe circumference on the inner circumferential side and an outercircumferential side gate mark portion located on the circumferenceclose to the outer circumferential side relative to the innercircumferential side gate mark portion. This first member is molded byinjecting a resin from the inner circumferential side gate located onthe circumference on the inner circumferential side in the space for ashroud and also from the outer circumferential side gate located on thecircumference close to the outer circumferential side relative to theinner circumferential side gate. Therefore, in the first member havingsuch a gate mark, uneven shrinkage of the shroud in the radial directioncaused by existence of the first blade can be suppressed for the samereason. Accordingly, the uniformity of the shape of the shroud can beimproved, thereby allowing sufficient welding between the second memberand the first member that includes the shroud and the first blade.Consequently, excellent durability and strength can be achieved whilestable air-blowing performance can be exhibited.

In the above-described impeller, the inner circumferential side gatemark portion has a plurality of inner circumferential side gate markswhile the outer circumferential side gate mark portion has a pluralityof outer circumferential side gate marks. The inner circumferential sidegate marks and the outer circumferential side gate marks that arelocated on the same plane are equal in number, and a corresponding oneof the inner circumferential side gate marks and a corresponding one ofthe outer circumferential side gate marks are located on the samestraight line extending in a radial direction on the same plane.

The inner circumferential side gate mark portion has a plurality ofinner circumferential side gate marks and the outer circumferential sidegate mark portion has a plurality of outer circumferential side gatemarks, thereby allowing a resin to evenly spread in the circumferentialdirection at the time of molding of each member. Accordingly, thehomogeneity of the first member (the second member) is improved.Furthermore, the inner circumferential side gate marks and the outercircumferential side gate marks that are located on the same plane areequal in number, and a corresponding one of the inner circumferentialside gate marks and a corresponding one of the outer circumferentialside gate marks are located on the same straight line extending in theradial direction on the same plane. Thereby, at the time when eachmember is molded, the flow of the resin coming from the outercircumferential side gate exerts a great influence upon the flow of theresin coming from the inner circumferential side gate. This causes agreater disturbance in the flow of the resin coming from the innercircumferential side gate into the space of the molding die. Therefore,the orientation of the filler in the space for the first blade or thespace for the second blade can be further suppressed, so that unevenshrinkage of the shroud (main plate) in the radial direction caused byexistence of the first blade (second blade) can be suppressed.

In the above-described impeller, at least one of the plurality of outercircumferential side gate marks has an elliptical shape.

In the case where the outer circumferential side gate is provided suchthat the resin injected from the outer circumferential side gate flowsin the circumferential direction of the main plate (shroud), the outercircumferential side gate mark thereof is formed in an elliptical shape.When the resin injected from the outer circumferential side gate flowsin the circumferential direction, the orientation of the filler on theouter circumferential side is to extend along the circumferentialdirection rather than the radial direction. Accordingly, the orientationof the filler in the space for the second blade, particularly theorientation of the filler on the outer circumferential side, can besufficiently suppressed, so that the above-described resistance causedby the orientation of the filler can be reduced.

In the above-described impeller, at least one of the first member andthe second member is integrally molded by injecting a resin containing afibrous filler from a position of the inner circumferential side gatemark portion and injecting a resin containing a spherical filler from aposition of the outer circumferential side gate mark portion.

At the time of molding, the resin containing a spherical filler isinjected from the outer circumferential side gate, thereby suppressingorientation of the fibrous filler on the outer circumferential side.Accordingly, the above-described resistance caused by the orientation ofthe filler can be reduced.

A water heater of the present invention includes: a burner generatingcombustion gas; a heat exchanger heating water flowing through inside byheat exchange with combustion gas; and a fan suctioning combustion gashaving passed through the heat exchanger and emitting combustion gas tooutside of the water heater. The fan includes a fan case, an impellerhoused within the fan case, a drive source attached outside the fancase, and a rotation shaft coupling the impeller and the drive source.The fan case has a back surface wall provided with a through hole. Theimpeller is arranged so as to have the second back surface facing theback surface wall. A gap through which air outside the fan case issuctioned into the fan case is provided between the rotation shaftpenetrating the through hole and the back surface wall. The impellerincluded in this water heater is the impeller as described above.

According to the water heater of the present invention, the air-blowingcapability of the fan can be achieved by the air-blowing force of thefirst blade of the impeller while the drive source can be cooled andbackflow of combustion gas can be prevented by the air-blowing force ofthe second blade of the impeller. Furthermore, since the impeller isexcellent in durability and strength and also can exhibit stableair-blowing performance, excellent fan performance can be achieved.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view schematically showing the configuration of awater heater in the first embodiment.

FIG. 2 is a partial cross-sectional side view schematically showing theconfiguration of the water heater shown in FIG. 1.

FIG. 3 is a partial cross-sectional view schematically showing a fan andan exhaust box in the first embodiment.

FIG. 4 is a side view schematically showing the configuration of animpeller in the first embodiment.

FIG. 5 is a perspective view schematically showing the configuration ofthe impeller in the first embodiment.

FIG. 6 is a cross-sectional view schematically showing the configurationof the impeller in the first embodiment.

FIG. 7 is an exploded plan view for illustrating the configuration ofthe first blade included in the impeller of the water heater shown inFIG. 1.

FIG. 8 is a plan view for illustrating the configuration of the secondblade included in the impeller of the water heater shown in FIG. 1.

FIG. 9 is a perspective view schematically showing a constituentmaterial of the impeller in the first embodiment.

FIG. 10 is another diagram schematically showing the constituentmaterial of the impeller shown in FIG. 9.

FIG. 11 is a perspective view schematically showing another constituentmaterial of the impeller in the first embodiment.

FIG. 12 is a perspective view schematically showing the constituentmaterial of the impeller shown in FIG. 11 as seen from a differentdirection.

FIG. 13 is a diagram schematically showing the state of an end face of alinearly protruding region in the first blade before welding.

FIG. 14 is a cross-sectional view schematically showing the state wheretwo constituent materials of the impeller are combined.

FIG. 15 is a cross-sectional view schematically showing the state at thetime of welding of the main plate and the first blade according to thefirst embodiment.

FIG. 16 is a schematic cross-sectional view of a weld portion.

FIG. 17 is a schematic cross-sectional view of a non-weld portion.

FIG. 18 is a cross-sectional view schematically showing the state at thetime of welding of the main plate and the first blade in the secondembodiment.

FIG. 19 is a cross-sectional view schematically showing the state at thetime of welding of the main plate and the first blade in the thirdembodiment.

FIG. 20 is a cross-sectional view schematically showing theconfiguration of an impeller in the fourth embodiment.

FIG. 21 is a plan view schematically showing the impeller in the fourthembodiment in plan view as seen from the direction orthogonal to thesecond plane of the main plate.

FIG. 22 is a plan view schematically showing an impeller in the fifthembodiment in plan view as seen from the direction orthogonal to thesecond plane of the main plate.

FIG. 23 is a partial cross-sectional view schematically showing theconfiguration of the impeller in the fifth embodiment.

FIG. 24 is a plan view schematically showing another configuration ofthe impeller in the fifth embodiment in plan view as seen from thedirection orthogonal to the second plane of the main plate.

FIG. 25 is a side view schematically showing the configuration of animpeller in the sixth embodiment.

FIG. 26 is a cross-sectional view schematically showing theconfiguration of the impeller in the sixth embodiment.

FIG. 27 is a perspective view schematically showing the configuration ofthe first member of the impeller in the sixth embodiment.

FIG. 28 is a front view schematically showing the configuration of thefirst member in the sixth embodiment.

FIG. 29 is a front view schematically showing the configuration of thefirst blade in the first member in the sixth embodiment.

FIG. 30 is a perspective view schematically showing the configuration ofthe second member of the impeller in the sixth embodiment.

FIG. 31 is a front view schematically showing the configuration of thesecond member in the sixth embodiment.

FIG. 32 is a front view schematically showing the configuration of thesecond blade in the second member in the sixth embodiment.

FIG. 33 is a schematic diagram for illustrating the relation between aspace within a molding die for molding the first member and the positionof a gate.

FIG. 34 is a schematic cross-sectional view taken along a line A-A′ inFIG. 33 showing the state where a resin is injected into the spacewithin the molding die and into the gate.

FIG. 35 is a schematic diagram for illustrating the relation between thespace within the molding die for molding the second member and theposition of the gate.

FIG. 36 is a schematic cross-sectional view taken along a line A-A′ inFIG. 35 showing the state where a resin is injected into the spacewithin the molding die and into the gate.

FIG. 37 is a front view schematically showing the configuration of thesecond member in which an outer circumferential side gate mark has anelliptical shape.

FIG. 38 is a schematic diagram for illustrating the relation between thespace within the molding die for molding the second member shown in FIG.37 and the position of the gate.

FIG. 39 is a schematic diagram showing the state shown in FIG. 38 asseen from a different direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be hereinafter describedwith reference to the accompanying drawings, in which the same orcorresponding components are designated by the same referencecharacters. Furthermore, the dimensional relation of a length, a width athickness, a depth, and the like is modified as appropriate for thepurpose of clarifying and simplifying each figure, and is not to actualscale. In each figure, the same components are designated by the samereference characters, and description thereof will not be repeated.

First Embodiment

(Configuration)

The configuration of a fan and a water heater in the first embodimentwill be hereinafter described with reference to FIGS. 1 to 8. In eachfigure, the same components are designated by the same referencecharacters, and description thereof will not be repeated.

Referring mainly to FIGS. 1 and 2, a water heater 100 of the presentembodiment serves as a water heater of a latent heat recovery typeadapted to an exhaust suction and combustion system. This water heater100 mainly includes a housing 1, a burner 2, a primary heat exchanger 3,a secondary heat exchanger 4, an exhaust box 5, a fan 6, an exhaust tube7, a drainage water tank 8, and pipes 9 to 15.

Burner 2 serves to produce a combustion gas by burning a fuel gas. A gassupply pipe 10 is connected to burner 2. This gas supply pipe 10 servesto supply a fuel gas to burner 2. A gas valve (not shown) implemented,for example, by an electromagnetic valve is attached to this gas supplypipe 10.

A spark plug 2 a is arranged above burner 2. This spark plug 2 a servesto ignite an air fuel mixture injected from burner 2 to thereby producea flame, by generating sparks between the plug and a target (not shown)provided in burner 2. Burner 2 generates a quantity of heat by burning afuel gas supplied from gas supply pipe 10 (which is called a combustionoperation).

Referring mainly to FIG. 2, primary heat exchanger 3 is a heat exchangerof a sensible heat recovery type. This primary heat exchanger 3 mainlyhas a plurality of plate-shaped fins 3 b, a heat conduction pipe 3 apenetrating the plurality of plate-shaped fins 3 b, and a case 3 caccommodating fins 3 b and heat conduction pipe 3 a. Primary heatexchanger 3 exchanges heat with the combustion gas generated by burner2, and specifically, serves to heat water which flows through heatconduction pipe 3 a of primary heat exchanger 3 with the quantity ofheat generated as a result of the combustion operation of burner 2.

Referring mainly to FIG. 2, secondary heat exchanger 4 is a heatexchanger of a latent heat recovery type. This secondary heat exchanger4 is located downstream of primary heat exchanger 3 in a flow of thecombustion gas and connected in series with primary heat exchanger 3.Since water heater 100 according to the present embodiment thus hassecondary heat exchanger 4 of a latent heat recovery type, it is a waterheater of the latent heat recovery type.

Secondary heat exchanger 4 mainly has a drainage water discharge port 4a, a heat conduction pipe 4 b, a sidewall 4 c, a bottom wall 4 d, and anupper wall 4 g. Heat conduction pipe 4 b is layered as it is spirallywound. Sidewall 4 c, bottom wall 4 d, and upper wall 4 g are arranged tosurround heat conduction pipe 4 b.

In secondary heat exchanger 4, water flowing through heat conductionpipe 4 b is pre-heated (heated) through heat exchange with thecombustion gas of which heat has been exchanged in primary heatexchanger 3. As a temperature of the combustion gas is lowered toapproximately 60° C. through this process, moisture contained in thecombustion gas is condensed so that latent heat can be obtained. Inaddition, latent heat is recovered in secondary heat exchanger 4 andmoisture contained in the combustion gas is condensed, thereby producingdrainage water.

Bottom wall 4 d serves as a partition between primary heat exchanger 3and secondary heat exchanger 4, and also serves as an upper wall ofprimary heat exchanger 3. This bottom wall 4 d is provided with anopening 4 e that allows communication between a space where heatconduction pipe 3 a of primary heat exchanger 3 is arranged and a spacewhere heat conduction pipe 4 b of secondary heat exchanger 4 isarranged. As shown with hollow arrows in FIG. 2, the combustion gas canflow from primary heat exchanger 3 to secondary heat exchanger 4 throughopening 4 e. In this embodiment, for the sake of simplification,although one common component is employed for bottom wall 4 d ofsecondary heat exchanger 4 and the upper wall of primary heat exchanger3, an exhaust collection and guide member may be connected betweenprimary heat exchanger 3 and secondary heat exchanger 4.

Furthermore, upper wall 4 g is provided with an opening 4 h. Thisopening 4 h allows communication between the space where heat conductionpipe 4 b of secondary heat exchanger 4 is arranged and an internal spacein exhaust box 5. As shown with hollow arrows in FIG. 2, the combustiongas can flow from secondary heat exchanger 4 into the internal space inexhaust box 5 through opening 4 h.

Drainage water discharge port 4 a is provided in sidewall 4 c or bottomwall 4 d. This drainage water discharge port 4 a opens at a lowestposition in the space surrounded by side wall 4 c, bottom wall 4 d andupper wall 4 g (at a lowermost position in a vertical direction in thestate where the water heater is placed), which is lower than thelowermost end of heat conduction pipe 4 b. Thus, drainage water producedin secondary heat exchanger 4 can be guided to drainage water dischargeport 4 a along bottom wall 4 d and sidewall 4 c as shown with blackarrows in FIG. 2.

Referring mainly to FIGS. 2 and 3, exhaust box 5 forms a path for a flowof the combustion gas between secondary heat exchanger 4 and fan 6. Thisexhaust box 5 can guide the combustion gas of which heat has beenexchanged in secondary heat exchanger 4 to fan 6. Exhaust box 5 isattached to secondary heat exchanger 4 and located downstream ofsecondary heat exchanger 4 in the flow of the combustion gas.

Exhaust box 5 mainly has a box main body 5 a and a fan connectionportion 5 b. The internal space of box main body 5 a communicatesthrough opening 4 h of secondary heat exchanger 4 with the internalspace in which heat conduction pipe 4 b of secondary heat exchanger 4 isdisposed. Fan connection portion 5 b is provided so as to protrude fromthe upper portion of box main body 5 a. This fan connection portion 5 bhas a cylindrical shape, for example, and has an internal space 5 b athat communicates with the internal space of box main body 5 a.

Referring mainly to FIGS. 1 and 3, fan 6 mainly has a fan case 61, animpeller 62, a drive source 63, and a rotation shaft 64. Fan 6 serves toemit the combustion gas (of which heat has been exchanged in secondaryheat exchanger 4) which has passed through secondary heat exchanger 4 tothe outside of water heater 100 by suctioning the combustion gas, andthis fan is connected to exhaust tube 7 leading to the outside of waterheater 100.

This fan 6 is located downstream of exhaust box 5 and secondary heatexchanger 4 in the flow of the combustion gas. Namely, in water heater100, burner 2, primary heat exchanger 3, secondary heat exchanger 4,exhaust box 5, and fan 6 are arranged in this order from upstream todownstream in the flow of the combustion gas produced in burner 2. Sincethe combustion gas is suctioned and exhausted by means of fan 6 as abovein this arrangement, water heater 100 in the present embodiment is awater heater of an exhaust suction and combustion type.

Referring mainly to FIG. 3, fan case 61 mainly includes a back surfacewall 61 a provided with a through hole 61 c and a circumferential wall61 b surrounding back surface wall 61 a, and has an internal space 61 din which impeller 62 is housed in a rotatable manner. In FIG. 3,although back surface wall 61 a and circumferential wall 61 b are formedby different members, back surface wall 61 a and circumferential wall 61b may be integrally formed.

Referring mainly to FIGS. 3 to 6, impeller 62 is housed within fan case61 (on one side of back surface wall 61 a). Impeller 62 mainly has adisc-shaped main plate 620, a plurality of first blades 621, a pluralityof second blades 622, a shroud 623, and a boss portion 624.

Main plate 620 has a first plane 620 a and a second plane 620 b on theside opposite to first plane 620 a. A plurality of first blades 621 areprovided on first plane 620 a while a plurality of second blades 622 areprovided on second plane 620 b. Shroud 623 is provided so as to entirelycover the plurality of first blades 621, and provided in its centerportion with an opening 623 c.

Furthermore, a boss portion 624 protruding from first plane 620 a isprovided in the center portion of first plane 620 a of main plate 620.Boss portion 624 is provided in its center portion with a bearing hole624 a passing therethrough from the first plane 620 a side to the secondplane 620 b side (FIG. 6). When rotation shaft 64 penetrates thisbearing hole 624 a, impeller 62, rotation shaft 64 and drive source 63can be connected.

Referring mainly to FIGS. 3 and 4, impeller 62 is arranged within fancase 61 such that first plane 620 a is located on the fan connectionportion 5 b side opposite to back surface wall 61 a (on one side of backsurface wall 61 a). Furthermore, as shown in FIG. 3, shroud 623 isarranged such that its opening 623 c faces internal space 5 b a whilesecond blade 622 is arranged so as to face back surface wall 61 a.

According to the above-described configuration, by the air-blowingcapability of first blade 621, combustion gas can be suctioned from boxmain body 5 a of exhaust box 5 through fan connection portion 5 b intofan case 61, as shown by the hollow arrows in FIG. 3. In other words, inthe present embodiment, by means of rotation of impeller 62, thecombustion gas within exhaust box 5 is suctioned from the innercircumferential side of first plane 620 a of impeller 62 and emitted tothe outer circumferential side thereof.

In addition, the plurality of first blades 621 are covered by shroud 623having opening 623 c, thereby allowing improvement in the air-blowingcapability of the fan as compared with the case where shroud 623 is notprovided.

Referring mainly to FIG. 6, first blades 621 each are formed so as toextend from the inner circumferential side to the outer circumferentialside of first plane 620 a of the main plate and to protrude from firstplane 620 a. First blades 621 are separately provided on first plane 620a and do not come in contact with each other.

Each first blade 621 includes: a linearly protruding region (a region Ain FIG. 6) that is linearly increased in height from the outercircumferential side toward the inner circumferential side; and acurvedly protruding region (a region B in FIG. 6) that is curvedlyincreased in height from the outer circumferential side toward the innercircumferential side, this height extending in the direction in whichfirst blade 621 protrudes from first plane 620 a. In first plane 620 a,the curvedly protruding region is located closer to the innercircumferential side than the linearly protruding region is. Thelinearly protruding region is welded to main plate 620. Furthermore, thecurvedly protruding region of first blade 621 is defined as a non-weldregion that is not welded to main plate 620.

Referring mainly to FIGS. 6 and 7, when first plane 620 a is seen fromthe axial direction of rotation shaft 64 (an axis A shown by analternate long and short dash line in FIG. 3), first blade 621 has alength including: a linearly extending region linearly extending fromthe outer circumferential side to the inner circumferential side offirst plane 620 a (a region C in FIG. 7); and a curvedly extendingregion curvedly extending from the outer circumferential side to theinner circumferential side of first plane 620 a (a region D in FIG. 7).The curvedly extending region is located closer to the innercircumferential side than the linearly extending region is.

Thereby, the flow passage between first blades 621 adjacent to eachother is formed so as to be curved in the rotation direction of mainplate 620 on the suctioning side (inner circumferential side) and formedto have a linear flow passage on the emitting side (outercircumferential side). In addition, the direction in which the curvedlyextending region is curved is the same as the rotation direction of mainplate 620 (indicated by a hollow arrow in FIG. 7).

Furthermore, the length of first blade 621 in the direction in whichthis first blade 621 protrudes from first plane 620 a (the distancebetween a position at which first blade 621 is in contact with firstplane 620 a and a portion of first blade 621 that is farthest away fromfirst plane 620 a in the axial direction of this position) is defined asa “height” of first blade 621. The same also applies to second blade622. In the present specification, the distance between both ends offirst blade 621 extending from the inner circumferential side to theouter circumferential side of main plate 620 (the distance extendingalong the line appearing where first blade 621 and first plane 620 acome in contact with each other) is defined as a “length” of first blade621. The same also applies to second blade 622.

According to the above-described configuration, relative to rotatingimpeller 62, the inlet port of the flow passage is curved in therotation direction of impeller 62, thereby allowing the combustion gasto more efficiently flow into the flow passage. Furthermore, on the gasemitting side on which the centrifugal force is more likely to beapplied to the combustion gas flowing through the flow passage, thedirection of the flow passage and the direction in which the centrifugalforce is applied can be oriented in a more similar direction.Accordingly, the combustion gas flowing toward the gas emitting side ismore efficiently accelerated by the centrifugal force. Therefore, theair-blowing capability of the fan is consequently improved.

Referring mainly to FIGS. 4 to 6, shroud 623 is spaced apart from firstplane 620 a, provided so as to entirely cover the ends of first blades621 in the direction in which each first blade 621 protrudes, andprovided in its center portion with opening 623 c.

The inner circumferential side of the plane of shroud 623 on the sideopposite to first blade 621 (a curvedly inclined region 623 b) has ashape curvedly inclined in the radial direction so as to correspond tothe shape of first blade 621. In this way, shroud 623 is generallyshaped to extend along the height of each blade to be covered, so as notto interfere with air flowing between the blades.

Referring mainly to FIGS. 6 and 8, second blades 622 each are formed soas to extend from the inner circumferential side to the outercircumferential side of second plane 620 b and also to protrude fromsecond plane 620 b. Second blades 622 are separately provided on firstplane 620 a and do not come in contact with each other. Furthermore,referring to FIG. 4, in impeller 62 of the present embodiment, when mainplate 620 is seen from the axial direction, each of second blades 622 islocated between first blades 621 adjacent to each other.

Furthermore, when main plate 620 is seen from the axial direction of therotation shaft, a portion including an outer circumferential end of eachof the plurality of first blades 621 is disposed in the radial directionof main plate 620. This radial direction means a direction of thestraight line extending on the first plane of main plate 620 and passingthrough the rotation shaft.

Furthermore, when main plate 620 is seen from the axial direction of therotation shaft, a portion including an outer circumferential end of eachof the plurality of second blades 622 is disposed in the radialdirection of main plate 620. This radial direction means a direction ofthe straight line extending on the second plane of main plate 620 andpassing through the rotation shaft.

Referring mainly to FIGS. 1 and 3, drive source 63 is provided outsidethe fan case 61 (on back surface wall 61 a on the side opposite toimpeller 62). In water heater 100 of the present embodiment, gap 65 abetween drive source 63 and back surface wall 61 a is in communicationwith gap 65 b between through hole 61 c and rotation shaft 64. In otherwords, gap 65 b between through hole 61 c provided in back surface wall61 a and rotation shaft 64 allows communication between the outside offan case 61 (gap 65 a between drive source 63 and back surface wall 61a) and the inside of fan case 61 (gap 65 c between back surface wall 61a and impeller 62).

Rotation shaft 64 penetrates through hole 61 c of fan case 61, therebycoupling impeller 62 housed within fan case 61 and drive source 63provided outside fan case 61. Accordingly, impeller 62 is provided withdrive force from drive source 63 and can rotate around rotation shaft64.

Referring mainly to FIG. 1, exhaust tube 7 is disposed outside waterheater 100, and connected to the outer circumferential side of fan case61. Accordingly, the combustion gas emitted to the outer circumferentialside by first blade 621 of impeller 62 can be emitted to the outside ofwater heater 100 through exhaust tube 7.

Referring mainly to FIG. 1, drainage water tank 8 serves to storedrainage water produced in secondary heat exchanger 4. This drainagewater tank 8 and drainage water discharge port 4 a of secondary heatexchanger 4 are connected by drainage water discharge pipe 9. The aciddrainage water stored in drainage water tank 8 is for exampletemporarily stored in the internal space of drainage water tank 8, andthen, usually discharged through a drainage water discharge pipe 14 tothe outside of water heater 100.

It is to be noted that the lower portion of drainage water tank 8 isconnected to a drainage water outlet pipe 15 separately from drainagewater discharge pipe 14. This drainage water outlet pipe 15 (usuallyclosed) is designed to be opened during maintenance or the like, therebyallowing discharge of the drainage water within drainage water tank 8that cannot be discharged through drainage water discharge pipe 14. Aninternal space in drainage water tank 8 may be filled with aneutralization agent (not shown) for neutralizing acid drainage water.

Referring mainly to FIG. 1, a gas supply pipe 10 is connected to burner2. Water supply pipe 11 is connected to heat conduction pipe 4 b ofsecondary heat exchanger 4 (see FIG. 2) and hot water delivery pipe 12is connected to heat conduction pipe 3 a of primary heat exchanger 3(see FIG. 2). Heat conduction pipe 3 a of primary heat exchanger 3 andheat conduction pipe 4 b of secondary heat exchanger 4 are connected toeach other through connection pipe 13. Each of gas supply pipe 10, watersupply pipe 11, and hot water delivery pipe 12 leads to the outside, forexample, in a top portion of water heater 100.

(Production of Impeller)

Then, production of an impeller will be hereinafter described withreference to FIGS. 9 to 17.

In the present embodiment, a first component 62A and a second component62B are first produced. First component 62A is provided as an integrallymolded product obtained by integrally molding shroud 623 and firstblades 621 as shown in FIGS. 9 and 10. Second component 62B is providedas an integrally molded product obtained by integrally molding mainplate 620, second blades 622 and boss portion 624 as shown in FIGS. 11and 12. First component 62A and second component 62B can be produced byvarious known integrally molding methods and the like.

Referring to FIGS. 10, 13 and 14, in first component 62A, a positioningprotrusion 621 f is formed at an end (end face) 621 c of the curvedlyprotruding region (B in FIG. 14) of first blade 621 on the side oppositeto shroud 623. Referring to FIG. 13, a melt portion 621 e is formed atend face 621 c of the linearly protruding region welded to main plate620. This melt portion is not formed in the curvedly protruding regionthat is not welded to main plate 620. Melt portion 621 e has atriangular shape as seen from an outer circumferential side end face 621d of first blade 621.

Referring to FIG. 11, in second component 62B, first plane 620 a of mainplate 620 is provided with a plurality of holes 620 d and a plurality ofpositioning concave portions (grooves) 620 c. In plan view showing mainplate 620 as seen from the direction orthogonal to first plane 620 a,hole 620 d and groove portion 620 c each are located between secondblades 622 adjacent to each other. It is to be noted that hole 620 d maypenetrate main plate 620 (see FIG. 12).

When shroud 623 is pressed by an ultrasonic welding jig and applied withultrasonic vibration in the state where first component 62A and secondcomponent 62B are overlaid on each other such that each first blade 621and main plate 620 come into contact with each other, each first blade621 and main plate 620 are ultrasonic-welded to each other, therebyproducing an impeller. Although details will be hereinafter described,the configuration and the like of each part are the same as those inFIG. 5, and therefore, detailed description thereof will not berepeated.

Referring to FIG. 9, the outer circumferential side of the plane ofshroud 623 on the side opposite to first blade 621 (linearly inclinedregion 623 a) has a shape linearly inclined in the radial direction soas to correspond to the shape of first blade 621. Ultrasonic welding iscarried out in the state where linearly inclined region 623 a is pressedby the jig produced so as to conform to the shape of this linearlyinclined region 623 a. It is preferable that the plane of linearlyinclined region 623 a on the side opposite to first blade 621 isinclined at an angle of 30° or less to main plate 620. This is becausevertical ultrasonic vibration from the jig of the ultrasonic weldingmachine can be more stably transmitted to the weld portion when theplane is inclined in the direction closer to the horizontal direction.

Referring to FIG. 10, a plurality of end faces 621 c of first blades 621on the side opposite to shroud 623 are located in a range of one flatplane. Thereby, the plurality of end faces 621 c can be brought intocontact with first plane 620 a of disc-shaped main plate 620 at the timeof ultrasonic welding. It is to be noted that end face 621 c of thecurvedly protruding region of each first blade 621 can be brought intocontact with main plate 620 but is not welded thereto. This is becauseend face 621 c is neither pressed by the jig of the ultrasonic weldingmachine nor provided with positioning concave portion 620 c of mainplate 620.

Referring to FIG. 13, melt portion 621 e is formed on end face 621 c ofthe linearly protruding region that is welded to main plate 620. Thismelt portion is not formed in the curvedly protruding region that is notwelded to main plate 620. This can further ensure that main plate 620can be welded to the linearly protruding region of first blade 621, andalso, main plate 620 can be prevented from being welded to the curvedlyprotruding region of first blade 621.

Melt portion 621 e has a triangular shape as seen from outercircumferential side end face 621 d of first blade 621. It is preferablethat melt portion 621 e has a triangular shape in which the angle of theapex closer the inner circumferential side is more acute. Consequently,the melt portion can be melted in a similar manner on each of the innercircumferential side and the outer circumferential side of the linearlyprotruding region, so that stable welding strength can be achieved.

When first component 62A and second component 62B are overlaid on eachother, protrusion 621 f is fitted in hole 620 d provided in the firstplane of main plate 620 as shown in FIG. 14. Thereby, positionalmisalignment of the curvedly protruding region (non-weld region) offirst blade 621 can be prevented. Furthermore, the plurality of firstblades 621 of first component 62A are respectively inserted into andwelded to a plurality of positioning concave portions 620 c of secondcomponent 62B. Thereby, the positional misalignment between main plate620 and each first blade 621 at the time of welding can be prevented, sothat welding strength can be improved.

Referring to FIGS. 11 and 12, when main plate 620 is seen from the axialdirection of rotation shaft 64, each second blade 622 is placed so as tobe located between two positioning concave portions 620 c adjacent toeach other. During ultrasonic welding, main plate 620 is placed on a jig66 on the receiving side of the welding machine in the state wheresecond plane 620 b is located on the underside (see FIG. 15). In thiscase, jig 66 on the receiving side is formed in a disc shape or the likeand has a size equal to or greater than the size of main plate 620. Anotch portion in a slit shape is provided at the position correspondingto second blade 622. At the time of welding, main plate 620 is placedsuch that each second blade 622 is inserted into the notch portion ofjig 66 and second plane 620 b comes into contact with the main surfaceof jig 66 other than the notch portion. Accordingly, the notch portionof jig 66 is designed so as to be deeper than the height of second blade622 in its protruding direction and to be larger than second blade 622.In this way, positioning concave portion 620 c serving as a weld portionbetween main plate 620 and first blade 621 is supported by jig 66 on thereceiving side of the welding machine from the second plane 620 b side(underside) of main plate 620. Accordingly, ultrasonic vibration can besufficiently transmitted to the weld portion, thereby allowingsufficient welding.

Then, referring to FIG. 15, the state at the time of welding of mainplate 620 and each first blade 621 in the present embodiment will behereinafter described. As described above, at the time of welding ofmain plate 620 and each first blade 621, main plate 620 is placed suchthat its second plane 620 b comes into contact with the upper surface ofjig 66 of the welding machine. Then, first component 62A formed of firstblades 621 and shroud 623 is overlaid on main plate 620 such that eachfirst blade 621 is located on the underside, and positioned by concaveportion 620 c (FIG. 11), protrusion 621 f (FIG. 10), hole 620 d (FIG.11) and the like. Then, jig 65 of the ultrasonic welding machine ispressed against shroud 623 from above, thereby implementing ultrasonicwelding between main plate 620 and each first blade 621.

In this case, the outer circumferential portion of shroud 623 has ashape that is linearly inclined in the radial direction of main plate620 so as to correspond to the shape of the linearly protruding regionof first blade 621. Accordingly, the end face of jig 65 on the shroud623 side can be readily processed to have a shape corresponding to theshape of linearly protruding region 621Aa of first blade 621. Then, jig65 of the ultrasonic welding machine is pressed against this outercircumferential portion (linearly inclined region), thereby improvingadhesiveness between jig 65 and shroud 623, so that ultrasonic vibrationcan be stably transmitted to the weld portion. Thereby, main plate 620and linearly protruding region 621Aa of first blade 621 can besufficiently welded.

It is to be noted that curvedly protruding region 621Ab of first blade621 may come in contact with main plate 620 but is not welded thereto.This is because end face 621 c of the curvedly protruding region offirst blade 621 is a portion that is not pressed by jig 65 of theultrasonic welding machine, and to which ultrasonic vibration in thevertical direction (in the direction perpendicular to the main plate) ishardly transmitted. Accordingly, variations in strength of weldingbetween the main plate and first blade 621 are suppressed, so that animpeller with stable quality can be produced. Consequently, the qualityof the fan can be stabilized. Even if ultrasonic welding is carried outin the state as shown in FIG. 15, there may be a possibility thatcurvedly protruding region 621Ab of first blade 621 and main plate 620are partially welded to each other by propagation of ultrasonicvibration, which is however not problematic if no quality variationoccurs in the fan.

Ultrasonic welding is a processing technique by which a thermoplasticresin is instantaneously melted and joined by minute ultrasonicvibration and welding pressure. Therefore, in the present embodiment,the constituent material of impeller 62 (a shroud, the first blade, amain plate, and the second blade) is made of a thermoplastic resin thatis melted as a result of heating by means of ultrasonic vibration.

Then, referring to FIGS. 16 and 17, an explanation will be given withregard to a difference between a portion that is welded between mainplate 620 and the linearly protruding region of first blade 621 (a weldportion) and a portion that is not welded between main plate 620 and thecurvedly protruding region of first blade 621 (a non-weld portion).

FIG. 16 is a diagram showing a weld portion. As shown in FIG. 16, in theweld portion between main plate 620 and the linearly protruding regionof first blade 621, a convex portion 620 cc is formed with a resinmelted by ultrasonic vibration or the like, for example, in positioningconcave portion 620 c or the like of the main plate. In this way, aportion having a shape different from the shape of the base material(main plate 620 and first blade 621) is generally formed in the weldportion between main plate 620 and first blade 621.

FIG. 17 is a diagram showing a non-weld portion. As shown in FIG. 17, inthe non-weld portion between main plate 620 and the curvedly protrudingregion of first blade 621, the resin is not melted by ultrasonicvibration or the like, but this non-weld portion is generally formedonly by the shape of the base material (main plate 620 and first blade621). In the non-weld portion, first blade 621 may or may not come incontact with main plate 620.

In this way, the weld portion and the non-weld portion can be identifiedalso in an impeller after production.

(Functions and Effects)

The functions and effects of the present embodiment will then bedescribed.

The impeller provided in the fan as described above: includes a linearlyprotruding region (a region A in FIG. 6) that is linearly increased inheight from the outer circumferential side toward the innercircumferential side; and a curvedly protruding region (a region B inFIG. 6) that is curvedly increased in height from the outercircumferential side toward the inner circumferential side, this heightextending in the direction in which first blade 621 protrudes from firstplane 620 a. The linearly protruding region is welded to main plate 620.According to this structure, the plane on the side opposite to thelinearly protruding region of shroud 623 is a flat plane (a linearlyinclined plane). Accordingly, by pressing the jig of the ultrasonicwelding machine against this flat plane portion (see FIG. 15), theadhesiveness between the jig and shroud 623 is improved, so thatultrasonic vibration can be stably transmitted to the weld portion.Therefore, main plate 620 and first blade 621 can be sufficientlywelded.

Also in the above-described impeller, the curvedly protruding region offirst blade 621 is defined as a non-weld region that is not welded tomain plate 620. When the curvedly protruding region is to be welded tomain plate 620, it is necessary to press the jig of the ultrasonicwelding machine against the curvedly inclined region of shroud 623 (aportion corresponding to the curvedly protruding region of the firstblade) to transmit ultrasonic vibration. However, ultrasonic vibrationcannot be sufficiently transmitted to a curved surface, thereby leadingto insufficient welding or causing welding strength variations, whichare therefore not preferable for a product. Accordingly, by not weldingthe curvedly protruding region to main plate 620, it becomes possible toproduce an impeller having stable quality but not undergoing strengthvariations of welding between main plate 620 and first blade 621.Consequently, the quality of the fan can be stabilized.

Also in the above-described impeller, when main plate 620 is seen fromthe axial direction, each of second blades 622 is located between firstblades 621 adjacent to each other. Thereby, when main plate 620 and eachfirst blade 621 are ultrasonic welded (see FIG. 15), the weld portionbetween main plate 620 and each first blade 621 is plane-supported byjig 66 in contact with the plane between adjacent second blades 622 onthe second plane side, so that the weld portion is held with stability.Accordingly, ultrasonic vibration can readily be sufficientlytransmitted to the weld portion. Therefore, main plate 620 and eachfirst blade 621 can be sufficiently welded. Particularly, in the casewhere second blade 622 is located at the same distance from each of twoadjacent first blades 621 when main plate 620 is seen from the axialdirection, main plate 620 is more stably held. Therefore, ultrasonicvibration can readily be more sufficiently transmitted to the weldportion. In addition, in the case where first blade 621 and second blade622 are overlapped with each other when main plate 620 is seen from theaxial direction, the second plane of main plate 620 cannot be supportedby jig 65. Consequently, main plate 620 cannot be stably held, so thatultrasonic vibration may be less likely to be sufficiently transmittedto the weld portion.

Furthermore, when main plate 620 is seen from the axial direction, eachof second blades 622 is located between first blades 621 adjacent toeach other. Thereby, it becomes possible to achieve an effect ofsuppressing resonance between the noise generated by rotation of firstblade 622 and the noise generated by rotation of second blade 622, sothat the noise generated by fan 6 can be reduced.

Furthermore, when main plate 620 is seen from the axial direction of therotation shaft, a portion including an outer circumferential end of eachof the plurality of first blades 621 is disposed in the radial directionof main plate 620. This allows airflow to smoothly flow in the directionalong the centrifugal force, which is caused by rotation of theimpeller, in the outer circumferential portion onto which thecentrifugal force is greatly exerted. Consequently, the weld portion isless likely to come off. As long as the above-described effect can beachieved, the linearly protruding region of first blade 621 may besomewhat deviated from the radial direction when main plate 620 is seenfrom the axial direction of the rotation shaft.

Furthermore, when main plate 620 is seen from the axial direction of therotation shaft, a portion including the outer circumferential end ofeach of the plurality of second blades 622 is disposed in the radialdirection of main plate 620. Accordingly, when main plate 620 is seenfrom the axial direction of the rotation shaft, each second blade 622can be readily disposed so as to be located between two first blades 621adjacent to each other. As long as the above-described effect can beachieved, second blade 622 may be somewhat deviated from the radialdirection when main plate 620 is seen from the axial direction of therotation shaft.

Furthermore, referring to FIGS. 7 and 8, the number of first blades 621is the same as the number of second blades 622 in the presentembodiment, but the numbers thereof are not limited thereto. However, ifthe number of first blades 621 is different from the number of secondblades 622, it is preferable that the number of second blades 622 is asubmultiple of the number of first blades 621. It is preferable thatsuch number of first blades 621 and second blades 622 are provided suchthat first blades 621 are arranged at regular intervals so as to besymmetrical with respect to the rotation shaft while second blades 622are arranged at regular intervals so as to be symmetrical with respectto the rotation shaft. Thereby, the air-blowing performance of the fanis stabilized.

Furthermore, the length of second blade 622 in the radial direction isnot particularly limited, but preferably equal to or greater than halfof the length of first blade 621 in the radial direction, and morepreferably equal to or greater than the length of the linearlyprotruding region of first blade 621. Even when the pressure within fancase 61 is particularly raised for some reasons, there hardly occurssuch a situation that the balance is disturbed to one side to causebackflow to occur only on the second blade 622 side.

Furthermore, in the present embodiment, the height of second blade 622is equal to or less than the height of first blade 621, and preferablyequal to or less than half of the height of first blade 621. When theheight of second blade 622 is increased, the air-blowing performance offirst blade 621 is lowered, and also, excessively incoming air may exertan influence upon the flow of the combustion gas. In addition, inimpeller 62 of the present embodiment, the height of second blade 622 isfixed in a range from the outer circumferential side to the innercircumferential side, but not limited thereto.

Furthermore, in water heater 100 of the present embodiment, by theair-blowing capability of first blade 621, combustion gas can besuctioned from box main body 5 a of exhaust box 5 through fan connectionportion 5 b into fan case 61. In other words, in water heater 100 of thepresent embodiment, by means of rotation of impeller 62, the combustiongas within exhaust box 5 is suctioned into the inner circumferentialside of first plane 620 a of impeller 62 and emitted to the outercircumferential side thereof (see hollow arrows in FIG. 3). This allowsthe fan to exert the air-blowing capability for causing the combustiongas of water heater 100 to flow from the downstream to the upstream.

Furthermore, in water heater 100 of the present embodiment, the airoutside the fan case 61 can be suctioned into fan case 61 by theair-blowing capability of second blade 622. In other words, in waterheater 100 of the present embodiment, by rotation of impeller 62, theair outside the fan case 61 is suctioned through the through hole 61 cinto fan case 61, and further emitted from the inner circumferentialside toward the outer circumferential side of second plane 620 b (seeblack arrows in FIG. 3). Accordingly, drive source 63 can be cooled.

Furthermore, by the air-blowing capability of second blade 622,resistance pressure resisting the flow of gas moving from the outercircumferential side to the inner circumferential side of second plane620 b is generated in gap 65 c between back surface wall 61 a andimpeller 62. In other words, water heater 100 of the present embodimentallows resistance pressure to be kept so as to resist the flow of thecombustion gas that is to flow from the inside to the outside of fancase 61 (backflow). Therefore, according to the water heater of thepresent invention, when the pressure inside fan case 61 is increased dueto factors such as blockage of exhaust tube 7, backflow of thecombustion gas can be suppressed.

Furthermore, the water heater of the present embodiment is a waterheater of a latent heat recovery type capable of heating water byrecovering latent heat of combustion gas. In this case, since aciddrainage water is produced by recovery of latent heat, it isparticularly useful to provide a highly durable impeller that is capableof resisting acid drainage water.

Particularly, in the water heater of the present embodiment, theabove-described fan is attached such that the shroud side is located onthe side closer to the burner. The opening of the fan case is providedon the underside in order to allow the rising combustion gas to besuctioned therethrough, and the impeller is placed such that its shroudside is located on this opening side (underside). Accordingly, drainagewater is more likely to accumulate in the boundary portion existingbetween shroud 623 and first blade 621 and corresponding to the uppersurface side of shroud 623. Thus, shroud 623 and each first blade 621are integrally formed, and main plate 620 and each first blade 621(integrally formed with shroud 623) are welded, so that a weld portionwith low durability is located on the underside of main plate 620 (onthe burner side). Thereby, the weld portion is less likely to be exposedto drainage water, with the result that the weld portion can beprotected from corrosion caused by drainage water. Consequently, itbecomes possible to provide a water heater including a highly durablefan that can resist a high temperature environment.

It is preferable that the impeller is made of a thermoplastic resinhaving acid resistance. This allows further improvement in fandurability against drainage water produced by recovery of latent heat.

Examples of the thermoplastic resin having acid resistance may bepolyphenylene sulfide (PPS), syndiotactic polystyrene (SPS), polyvinylchloride (PVC), silicone resin, fluororesin such aspolytetrafluoroethylene, unsaturated polyester resin, polycarbonateresin, methacrylstyrene (MS) resin, methacryl resin, AS resin (styreneacrylonitrile copolymer), ABS resin (acrylonitrile, butadiene, styrenecopolymerization synthetic resin), phenol resin, epoxy resin, melamineresin, polyethylene, polypropylene, polystyrene, and polyethyleneterephthalate (PET).

For the same reason, it is preferable that other members such as fancase 61, exhaust box 5, and exhaust tube 7 each are made of a materialhaving acid resistance.

Furthermore, in the present embodiment, since water heater 100 of theexhaust suction and combustion type is employed as described above inthe present embodiment, a combustion operation by burner 2 can bestabilized as compared with a water heater of what is called a forcedexhaust type even though exhaust tube 7 is decreased in diameter, whichwill be described below.

In a water heater of what is called a forced exhaust type, a fan, aburner, a primary heat exchanger, and a secondary heat exchanger arearranged in this order from upstream to downstream in a flow of acombustion gas. Namely, the combustion gas produced in the burner iscaused to flow into an exhaust tube outside the water heater by the fanthrough the primary heat exchanger and the secondary heat exchanger.

The combustion gas forced out of the fan receives flow path resistanceproduced by the primary heat exchanger and the secondary heat exchangerbefore it reaches the exhaust tube. Therefore, a pressure with which thecombustion gas is sent immediately before the exhaust tube is lower bymagnitude comparable to this flow path resistance. Therefore, in orderto force the combustion gas into the exhaust tube smaller in diameter, afan blow pressure should be raised. When a fan blow pressure is raised,however, an internal pressure within a burner case becomes higher.Therefore, when a supply pressure of the combustion gas supplied to theburner is low, a combustion operation becomes unstable.

In contrast, according to the exhaust suction and combustion type in thepresent embodiment, burner 2, primary heat exchanger 3, secondary heatexchanger 4, and fan 6 are arranged in this order from upstream todownstream in the flow of the combustion gas. With this type, since apressure is negative on the upstream side of fan 6, a blow pressure byfan 6 does not have to be raised. Thus, since an internal pressurewithin the burner case can be maintained low even though exhaust tube 7is decreased in diameter, a combustion operation can be stabilized evenwhen a supply pressure of the combustion gas supplied to burner 2 islow.

In addition, although an example using ultrasonic welding as a weldingmethod has been described in the present embodiment, vibration weldingor thermal welding can be employed in addition to ultrasonic welding.

Second Embodiment

Referring to FIG. 18, the present embodiment is different from the firstembodiment in that a thickened portion 623 d is provided on the plane ofshroud 623 on the side opposite to first blade 621. Since the featuresother than the above are the same as those in the first embodiment,description thereof will not be repeated.

The plane of thickened portion 623 d on the side opposite to first blade621 is horizontal to main plate 620. Accordingly, in the presentembodiment, ultrasonic vibration in the vertical direction (thedirection perpendicular to the main plate) can be more stablytransmitted to the weld portion, so that the weld portion can be moresufficiently welded.

In addition, it is preferable that thickened portion 623 d is providedin a portion overlapped with first blade 621 as seen from the directionof the rotation shaft. For the purpose of improving the adhesiveness tothe jig of the ultrasonic welding machine so as to allow ultrasonicvibration to be readily transmitted, it is preferable that thickenedportion 623 d is provided over the entire circumference of shroud 623.

Third Embodiment

Referring to FIG. 19, the present embodiment is different from thesecond embodiment in that thickened portion 623 d consists of twoportions. Since the features other than the above are the same as thosein the second embodiment, description thereof will not be repeated. Inaddition, the plane of each thickened portion 623 d on the side oppositeto first blade 621 is horizontal to main plate 620.

In the present embodiment, the impeller can be reduced in weight thanthe impeller in the second embodiment while achieving the effectssimilar to those in the second embodiment.

Fourth Embodiment

The present embodiment is different in configuration of the impellerfrom the first embodiment, but other configurations are the same asthose in the first embodiment. Accordingly, the same description as thatin the first embodiment will not be repeated.

(Configuration)

Referring mainly to FIG. 20, impeller 62 mainly has a disc-shaped mainplate 620, a plurality of first blades 621, a plurality of second blades622, a shroud 623, and a boss portion 624. First blades 621, shroud 623,and boss portion 624 are the same as those in the first embodiment.

Referring mainly to FIGS. 20 and 21, second blades 622 each are formedso as to extend from the inner circumferential side to the outercircumferential side of second plane 620 b and also to protrude fromsecond plane 620 b. Second blades 622 are separately provided on secondplane 620 b and do not come in contact with each other. In the presentembodiment, second blade 622 is fixed in height and extends in thedirection along the radial direction of main plate 620.

Each second blade 622 is separated by a slit 622 c into an inner blademember 622 a located on the inner circumferential side of second plane620 b and an outer blade member 622 b located on the outercircumferential side of second plane 620 b. The width of slit 622 c (thedistance between the ends of inner blade member 622 a and outer blademember 622 b facing each other) is not particularly limited. If thiswidth is too large, however, the length of the blade becomes too short,so that the function of second blade 622 may deteriorate. Accordingly,the width of the slit is preferably narrow.

In the present embodiment, a resin containing a fibrous filler is usedas a material forming first component 62A and second component 62B. Aglass fiber can be used as a fibrous filler. Furthermore, athermoplastic resin having acid resistance can be used as a resin. Athermoplastic resin having acid resistance is the same as the resinsmentioned in the first embodiment.

Impeller 62 of the present embodiment can be produced by welding: thefirst component including first blades 621 and shroud 623; and thesecond component including main plate 620, second blades 622, and bossportion 624, as described above.

(Functions and Effects)

The functions and effects of impeller 62 according to the presentembodiment will be hereinafter described.

Second component 62B provided as one of components of impeller 62 andincluding disc-shaped main plate 620 and a plurality of second blades622 can be produced as described below.

First prepared is a molding die having a disc-shaped first internalspace (corresponding to the shape of the main plate) and a plurality ofsecond internal spaces protruding from the first internal space(corresponding to the shape of the second blade). Then, a resincontaining a fibrous filler is injected in so as to flow while spreadingfrom the center side of the molding die (the center side of the firstinternal space) toward the outside thereof (the outer circumferentialside of the first internal space). Then, this resin is cured.

During curing of the resin, this resin tends to shrink. Particularlywhen a disc-shaped component is produced using a resin, the resin tendsto shrink more in the radial direction. Accordingly, in order to improvethe flatness of disc-shaped main plate 620 after curing, the resininjected into the first internal space is required to evenly shrink inthe radial direction.

As to the resin injected into the above-described molding die, thefiller in the resin injected into the disc-shaped first internal spaceis more likely to spread, whereas the filler in the resin injected intothe second internal space is more likely to be oriented in the directionin which the second internal space extends. This is because the firstinternal space extends so as to cause the flow of resin to randomlyspread, whereas the second internal space is arranged so as to cause theresin to flow only in a certain direction (the direction in which thesecond internal space extends).

If a slit is not provided in second blade 622 extending in the radialdirection of main plate 620, the second internal space is formed in aslit shape that linearly extends in the radial direction of thedisc-shaped first internal space. In other words, the filler oriented inthe second internal space is to linearly extend in the radial directionof the first internal space.

In this case, the filler oriented in the second internal space (thefiller oriented in second blade 622) acts to strongly resist radialshrinkage of the resin within the first internal space (the resinforming main plate 620). This is because the filler oriented in thesecond internal space acts as a tension rod against radial shrinkage ofthe resin within the first internal space.

When strong resistance occurs against radial shrinkage of the resinwithin the first internal space, it becomes difficult to cause the resinforming main plate 620 to shrink in the radial direction evenly in theportion having second blade 622 and in the portion not having secondblade 622. Consequently, the resulting main plate 620 is to have lowflatness. If the flatness of main plate 620 is low, fixation ofcomponents 62A and 62B using a jig becomes unstable at the time ofultrasonic welding. Accordingly, ultrasonic vibration cannot be stablytransmitted to the weld portion, with the result that the weldingperformance between each first blade 621 and first plane 620 a of mainplate 620 is decreased.

If first blade 621 and main plate 620 are not sufficiently welded, thedurability of the impeller formed by welding first component 62A andsecond component 62B is decreased. Furthermore, the impeller having amain plate with low flatness exhibits low motion balance performance,thereby generating vibration and noise, so that stable air-blowingperformance cannot be exhibited.

In contrast, according to impeller 62 in the present embodiment, secondblade 622 extending in the radial direction of main plate 620 isseparated by slit 622 c into inner blade member 622 a located on theinner circumferential side of second plane 620 b and outer blade member622 b located on the outer circumferential side of second plane 620 b.

In this case, since the second internal space in a molding die is shapedso as to be divided into two sections in the radial direction of thefirst internal space, the filler oriented in the second internal spacehas less effect as a tension rod in comparison with the above-describedcase. In other words, resistance by the filler oriented in second blade622 against radial shrinkage of the resin can be reduced.

Therefore, according to impeller 62 of the present embodiment, unevenshrinkage of main plate 620 in the radial direction caused by existenceof second blade 622 can be suppressed. Thereby, the flatness of mainplate 620 can be increased, thereby allowing second component 62Bincluding main plate 620 and second blade 622 to be sufficiently weldedto another component (first component 62A), so that excellent durabilityand strength can be achieved while stable air-blowing performance can beexhibited.

In impeller 62 described above, when slit 622 c is provided at aposition on the outer circumferential side with respect to the positionat one half of the radius of main plate 620, the function as a tensionrod described above can be effectively reduced, so that the flatness ofmain plate 620 can be further improved. This is because when the resininjected into the disc-shaped internal space shrinks, the resin shrinksmore on the outer circumferential side of the disc than on the innercircumferential side thereof, in which case the resistance caused by thefiller oriented in the radial direction exerts a large influence.

However, if slit 622 c is provided at a position on the side excessivelyclose to the outer circumferential side, inner blade member 622 a isincreased in length, so that the above-described resistance tends to beincreased. Accordingly, it is preferable that the position of slit 622 cin the radial direction is set on the inner circumferential side at adistance of one third or more of the radius from the external end ofmain plate 620.

Furthermore, in impeller 62 as described above, when slit 622 c isprovided at a position on the inner circumferential side with respect tothe position at one half of the radius of main plate 620, deteriorationof the air-blowing capability of second blade 622 can be suppressed.This is because the influence of the air-blowing capability of secondblade 622 is remarkably exerted more on the outer circumferential sideof second blade 622 than on the inner circumferential side thereof.

However, if slit 622 c is provided on the side excessively close to theinner circumferential side, outer blade member 622 b is increased inlength, so that the above-described resistance tends to increase.Accordingly, it is preferable that the position of slit 622 c in theradial direction is set on the outer circumferential side at a distanceof one third or more of the radius from the center of main plate 620.

Furthermore, in impeller 62 as described above, first blade 621 andshroud 623 are also integrally molded by a resin containing a fibrousfiller. Accordingly, first component 62A and second component 62B eachcan be improved in strength by containing a fibrous filler. Furthermore,when first component 62A and second component 62B are formed using thesame material, ultrasonic vibration at the time of welding can befurther evenly transmitted.

Furthermore, a resin containing a fibrous filler is used for thematerial of impeller 62 and also the components forming impeller 62 canalso be sufficiently welded, so that the fan can be improved indurability and strength and can exhibit stable air-blowing performance.

Fifth Embodiment

The present embodiment is different in configuration of the impeller,particularly in configurations of the second impeller and the mainplate, from the fourth embodiment, and other configurations are the sameas those in the fourth embodiment. Accordingly, the same descriptionwill not be repeated.

(Configuration)

Referring mainly to FIG. 22, second blades 622 each are formed so as toextend from the inner circumferential side to the outer circumferentialside of second plane 620 b and also to protrude from second plane 620 b.Second blades 622 are separately provided on second plane 620 b and donot come in contact with each other. Furthermore, each second blade 622is fixed in height and crosses the radial direction of main plate 620.

In plan view as seen from the direction orthogonal to second plane 620 bof main plate 620, each second blade 622 is formed in a curved lineincluding: a first curved portion 622 d located on the innercircumferential side of second plane 620 b and having a relatively smallradius of curvature; and a second curved portion 622 e located on theouter circumferential side of second plane 620 b, extending continuouslyto first curved portion 622 d, and having a relatively large radius ofcurvature. Furthermore, the direction in which first curved portion 622d is curved is different from the direction in which second curvedportion 622 e is curved, and second blade 622 is formed entirely in anS-shape.

Referring mainly to FIGS. 22 and 23, boss portion 624 is formed so as tobe continuously increased in size from an end portion 624 a a of theboss portion toward an uprising portion 624 b b that extends from firstplane 620 a of boss portion 624. Furthermore, a plurality of thinnedportions 624 b are provided in boss portion 624 on the second plane 620b side so as to surround bearing hole 624 a.

In this case, end portion 624 a a means an end of boss portion 624located at a height that is farthest away from first plane 620 a.Furthermore, uprising portion 624 bb means a position at which theheight level of the surface of first plane 620 a is started to changewith respect to the tangent line of the flat plane of first plane 620 aof main plate 620 (a dotted line in FIG. 23). Furthermore, theexpression that “boss portion 624 is formed so as to be continuouslyincreased in size” means that the outer shape of the cross-section ofthe boss portion shown in FIG. 23 is continuously increased.

(Functions and Effects)

In impeller 62 in the present embodiment, second blade 622 extends so asto cross the radial direction of main plate 620.

In this case, in a molding die for producing second component 62B, thesecond internal space corresponding to second blade 622 has a shape thatcrosses the radial direction of the first internal space correspondingto main plate 620. This leads to a reduction in function of the filleroriented in the second internal space as a tension rod in comparisonwith the case where the second internal space linearly extends in theradial direction of the first internal space. In other words, theresistance by the filler oriented in second blade 622 against radialshrinkage of the resin can be reduced.

Therefore, according to impeller 62 of the present embodiment, unevenshrinkage of main plate 620 in the radial direction caused by existenceof second blade 622 can be suppressed. Consequently, since the flatnessof main plate 620 can be improved, second component 62B including mainplate 620 and each second blade 622 can be sufficiently welded toanother component (first component 62A). Therefore, excellent durabilityand strength can be achieved while stable air-blowing performance can beexhibited.

Furthermore, in the present embodiment, in order to increase thestrength, boss portion 624 is formed so as to be continuously increasedin size from end portion 624 aa of the boss portion toward uprisingportion 624 bb that extends from first plane 620 a of boss portion 624.

In this case, when a thinned portion is not provided in boss portion 624on the second plane 620 b side, the thickness of the resin forming aportion near uprising portion 624 b b of boss portion 624 is to begreater than the thickness of the resin forming a portion near endportion 624 aa of boss portion 624 and the thickness of the resinforming main plate 620.

In this case, the time required for the resin near uprising portion 624bb to completely cure is longer than the time required for the resin inother portions to completely cure. When the time required for curing isdifferent in each part of boss portion 624, anisotropy occurs inshrinkage of resin, with the result that a distortion occurs in bossportion 624 and its surrounding area.

In contrast, according to the present embodiment, a thinned portion isprovided in boss portion 624 on the second plane 620 b side. Thereby,the resin forming a portion near uprising portion 624 bb of boss portion624 and the resin forming a portion near end portion 624 aa of bossportion 624 can be provided to have a similar thickness as compared withthe case where a thinned portion is not provided. Accordingly, thedistortion as described above can be suppressed.

Therefore, according to boss portion 624 provided in impeller 62 of thepresent embodiment, strength can be improved while a distortion in theboss portion can be suppressed.

The present embodiment described above in greater detail is not limitedto the above-described manner. For example, in FIG. 22, second blade 622is formed entirely in a curved line, but second blade 622 may be formedin a linear shape and provided so as to cross the radial direction ofmain plate 620. Furthermore, a part of second blade 622 may be formed ina curved line. Also in this case, the same effects as those describedabove can be achieved.

However, if the extending direction of second blade 622 deviates greatlyfrom the radial direction of main plate 620, the air-blowing force ofsecond blade 622 is decreased. Accordingly, as in the second embodiment,it is preferable that second blade 622 has an S-shape in a plan viewshowing main plate 620 as seen from the direction orthogonal to secondplane 620 b. In this case, deviation of second blade 622 from the radialdirection of main plate 620 can be reduced while second blade 622 isentirely formed in a curved line.

Particularly, when the radius of curvature of second curved portion 622e of second blade 622 that is located on the outer circumferential sideis relatively small, the air-blowing force of second blade 622 can bemaintained high. This is because the shape of second blade 622 on theouter circumferential side exerts a great influence upon the air-blowingforce.

When second blade 622 is formed in an S-shape, a preferable radius ofcurvature can be determined based on the diameter of main plate 620. Forexample, when the diameter of main plate 620 is 150 mm, the radius ofcurvature of first curved portion 622 d is preferably about 16 mm whilethe radius of curvature of second curved portion 622 e is preferablyabout 80 mm

Furthermore, as shown in FIG. 24, second blade 622 having an S-shape maybe separated by a slit into inner blade member 622 a and outer blademember 622 b. In this case, the flatness of main plate 620 can befurther improved.

Furthermore, as shown in FIG. 24, a third blade 625 extending from theinner circumferential side to the outer circumferential side of secondplane 620 b may be provided between outer blade members 622 b. In thiscase, in addition to the air-blowing force of second blade 622, theair-blowing force of third blade 625 can be exerted on the second plane620 b side of main plate 620. Therefore, the effect of cooling drivesource 63 and the effect of preventing backflow of combustion gas can beimproved.

As shown in FIG. 24, it is preferable that the third blade extendsbetween outer blade members 622 b but does not extend between innerblade members 622 a. This is for the purpose of preventing theair-blowing force from being decreased because adjacent blades areexcessively close to each other on the inner circumferential side ofsecond plane 620 b.

Sixth Embodiment

The present embodiment is different in configuration of the impeller,particularly in configurations of the main plate, the shroud and thesecond blade, from the fourth embodiment, but other configurations arethe same as those in the fourth embodiment. Accordingly, the samedescription will not be repeated.

(Configuration)

The impeller of the present embodiment will be hereinafter describedwith reference to FIGS. 25 to 32. For ease of explanation in thefollowing, in the present embodiment, the plane of shroud 623 that facesmain plate 620 is defined as the first back surface; the plane of shroud623 on the side opposite to the first back surface is defined as thefirst front surface; the plane of main plate 620 that faces shroud 623(the plane to which the first blade is welded; first plane 620 a) isdefined as the second front surface; and the plane of main plate 620from which the second blade protrudes (second plane 620 b) is defined asthe second back surface. Also in the present embodiment, first member62A and second member 62B are integrally molded by a resin containing afibrous filler, and impeller 62 formed of first member 62A and secondmember 62B is configured by welding these members.

In plan view as seen from the direction orthogonal to the imaginaryplane extending across the outer circumferential end of first backsurface 623B, shroud 623 has an annular shape. As seen in a crosssection orthogonal to the imaginary plane extending across the outercircumferential end of first back surface 623B, shroud 623 has atruncated cone shape having a slope portion squeezed to a certainextent.

Referring mainly to FIG. 28, first front surface 623A of shroud 623 onthe side opposite to first back surface 623B is provided with an innercircumferential side gate mark portion 31 located on an imaginarycircumference E on the inner circumferential side; and an outercircumferential side gate mark portion 32 located on an imaginarycircumference F close to the outer circumferential side relative toinner circumferential side gate mark portion 31.

Inner circumferential side gate mark portion 31 has a plurality of innercircumferential side gate marks 31 a, which are located at regularintervals, for example, on circumference E. Furthermore, outercircumferential side gate mark portion 32 has a plurality of outercircumferential side gate marks 32 a, which are located at regularintervals, for example, on circumference F.

In the present embodiment, the plurality of inner circumferential sidegate marks 31 a may be located on a base 31 a b. This is because innercircumferential side gate marks 31 a each are located in a curvedportion of shroud 623 (see FIG. 26). Specifically, when first member 62Ais molded by integral molding which will be described later, in the casewhere the inner circumferential side gate is provided at the positioncorresponding to the curved portion of shroud 623, a space for base 31 ab is provided between the inner circumferential side gate and the spacefor shroud 623, thereby allowing a resin to be stably injected from theinner circumferential side gate.

In the present embodiment, inner circumferential side gate marks 31 aand outer circumferential side gate marks 32 a are equal in number.Furthermore, a corresponding one of inner circumferential side gatemarks 31 a and a corresponding one of outer circumferential side gatemarks 32 a are located on the same straight line EF extending in theradial direction on first front surface 623A. FIG. 28 shows that oneinner circumferential side gate mark 31 a and one outer circumferentialside gate mark 32 a are located on the same straight line EF, which alsoapplies to the case of other gate marks. In other words, one innercircumferential side gate mark 31 a is located on the imaginary straightline connecting the center of opening 623 c provided in shroud 623 (theposition shown by a black spot in FIG. 28) and one outer circumferentialside gate mark 32 a.

Referring mainly to FIG. 32, second blade 622 is separated by a slitinto outer blade member 622 b located on the outer circumferential sideof second back surface 620 b and inner blade member 622 a located closeto the inner circumferential side relative to outer blade member 622 b.Outer blade member 622 b is greater in radius of curvature than innerblade member 622 a, and outer blade member 622 b and inner blade member622 a are curved in different directions, thereby forming an S-shape asa whole. Furthermore, an intermediate blade member (the third blade) 625extending from the inner circumferential side toward the outercircumferential side of second back surface 620 b is provided betweenouter blade members 622 b adjacent to each other. In other words, theshape of second blade 622 of the present embodiment is similar to theshape of the second blade shown in FIG. 24 (another configuration in thefifth embodiment).

Referring mainly to FIG. 31, second front surface 620 a of main plate620 is provided with an inner circumferential side gate mark portion 51located on an imaginary circumference G on the inner circumferentialside; and an outer circumferential side gate mark portion 52 located onan imaginary circumference H close to the outer circumferential siderelative to inner circumferential side gate mark portion 51.

Inner circumferential side gate mark portion 51 has a plurality of innercircumferential side gate marks 51 a, which are located at regularintervals, for example, on circumference G. Furthermore, outercircumferential side gate mark portion 52 has a plurality of outercircumferential side gate marks 52 a, which are located at regularintervals, for example, on circumference H.

In the present embodiment, inner circumferential side gate marks 51 aand outer circumferential side gate marks 52 a are equal in number.Furthermore, a corresponding one of inner circumferential side gatemarks 51 a and a corresponding one of outer circumferential side gatemarks 52 a are located on the same straight line GH extending in theradial direction on second front surface 620 a. FIG. 31 shows that oneinner circumferential side gate mark 51 a and one outer circumferentialside gate mark 52 a are located on the same straight line GH, which alsoapplies to the case of other gate marks. In other words, one innercircumferential side gate mark 51 a is located on the imaginary straightline connecting the center of main plate 620 (the position shown by ablack spot in FIG. 31) and one outer circumferential side gate mark 52a.

(Production of Impeller)

One example of the method of producing impeller 62 of the presentembodiment will be hereinafter described with reference to FIGS. 33 to37. First member 62A as one of the components of impeller 62 can beintegrally molded as in the following manner.

Referring mainly to FIG. 33, first prepared is a molding die having aninternal space 200A including: a first internal space 300 (correspondingto the shape of shroud 623); and a plurality of second internal spaces400 protruding from first internal space 300 (corresponding to the shapeof first blade 622). Internal space 200A (a space including firstinternal space 300 and second internal space 400) of this molding diehas a shape corresponding to the shape of first member 62A to be molded.

The above-described molding die is further provided with a gate throughwhich a resin is injected into the space corresponding to the shape offirst member 62A. Specifically, a plurality of gates are provided so asto allow each end of the plurality of inner circumferential side gates310 a and the plurality of outer circumferential side gates 320 a tocommunicate with a portion corresponding to first front surface 623A ofshroud 623. In addition, as shown in FIG. 34, inner circumferential sidegates 310 a and outer circumferential side gates 320 a each are formedas a pin gate.

Inner circumferential side gates 310 a are located at regular intervalson the circumference on the inner circumferential side of first internalspace 300 while outer circumferential side gates 320 a are located atregular intervals on the circumference close to the outercircumferential side relative to inner circumferential side gates 310 a.Furthermore, one inner circumferential side gate 310 a and one outercircumferential side gate 320 a are located on the same radial line offirst internal space 300. Also, inner circumferential side gates 310 aand outer circumferential side gates 320 a are equal in number.

Referring mainly to FIG. 34, a resin containing a fibrous filler isinjected into internal space 200A through inner circumferential sidegate 310 a and outer circumferential side gate 320 a in molding dies 301and 302 in which internal space 200A described above and a gate areprovided. Accordingly, internal space 200A of molding dies 301 and 302is filled with a resin.

After internal space 200A and the gate in molding dies 301 and 302 arefilled with a resin, the resin is cured, and then, molding dies 301 and302 are removed, thereby separating the resin filling innercircumferential side gate 310 a and outer circumferential side gate 320a and the resin filling the internal space. This results inintegrally-molded first member 62A that is molded in a shape of internalspace 200A of the molding die and has a gate mark left at a positioncorresponding to the position of each end of inner circumferential sidegate 310 a and outer circumferential side gate 320 a.

Second member 62B as the other component of impeller 62 can also beintegrally molded by the method similar to that for first member 62A.

Specifically, referring to FIGS. 35 and 36, first prepared is a moldingdie having an internal space 200B that includes: a third internal space500 (corresponding to the shape of main plate 620); a plurality offourth internal spaces 610, 650 and 630 (corresponding to the shapes ofouter blade member 622 b, inner blade member 622 a and intermediateblade member 625, respectively) protruding from third internal space500; and a fifth internal space 700 (corresponding to the shape of bossportion 624). Internal space 200B (the space including third internalspace 500, fourth internal spaces 610, 650, 630, and fifth internalspace 700) of this molding die has a shape corresponding to the shape ofsecond member 62B to be molded. In addition, third internal space 500 isprovided on its upper surface side with a groove space 800 used forholding end 621 c of first blade 621 therein.

The above-described molding die is further provided with a gate throughwhich a resin is injected into the space corresponding to the shape ofsecond member 62B. Specifically, a plurality of gates are provided so asto allow each end of the plurality of inner circumferential side gates510 a and the plurality of outer circumferential side gates 520 a tocommunicate with a portion corresponding to second front surface 620 aof main plate 620. In addition, as shown in FIG. 36, innercircumferential side gates 510 a and outer circumferential side gates520 a each are formed as a pin gate.

Inner circumferential side gates 510 a are located at regular intervalson the circumference on the inner circumferential side of third internalspace 500 while outer circumferential side gates 520 a are located atregular intervals on the circumference close to the outercircumferential side relative to inner circumferential side gates 510 a.Furthermore, one inner circumferential side gate 510 a and one outercircumferential side gate 520 a are located on the same radial line ofthird internal space 500. Also, inner circumferential side gates 510 aand outer circumferential side gates 520 a are equal in number.

Referring mainly to FIG. 35, a resin containing a fibrous filler isinjected into internal space 200B through inner circumferential sidegate 510 a and outer circumferential side gate 520 a in molding dies 501and 502 in which internal space 200B described above and a gate areprovided. Accordingly, internal space 200B of molding dies 501 and 502is filled with a resin.

After internal space 200B and the gate in molding dies 501 and 502 arefilled with a resin, the resin is cured, and then, molding dies 501 and502 are removed, thereby separating the resin filling innercircumferential side gate 510 a and outer circumferential side gate 520a and the resin filling the internal space. This results inintegrally-molded second member 62B that is molded in a shape of theinternal space of the molding die and has a gate mark left at a positioncorresponding to the position of each end of inner circumferential sidegate 510 a and outer circumferential side gate 520 a.

Then, first member 62A and second member 62B that are integrally moldedare coupled to each other. It is preferable to employ theabove-described ultrasonic welding for this coupling.

(Functions and Effects)

The functions and effects of impeller 62 according to the presentembodiment will be hereinafter described.

As to a resin member integrally molded using a molding die, a resintends to shrink at the time of curing. Particularly when producing acomponent like a disc having a shape increased in area in thecircumferential direction, the resin tends to shrink more in the radialdirection. Accordingly, in order to improve the uniformity of the shapeof the component after curing, the resin injected into the molding dieis required to evenly shrink in the radial direction.

Conventionally, when a resin product having a disc-shaped component ismolded, a resin flows while spreading from the inner circumferentialside toward the outer circumferential side, so that the uniformity ofthe shape can be improved. This is the reason why a molding die providedwith a gate at a portion corresponding to the inner circumferential sideof a disc-shaped component (a portion close to the center) has beenused. The resin member integrally molded by this method is to have agate mark located on the inner circumferential side of the disc.

It has been however found that the uniformity of the shape of main plate620 is greatly deteriorated in the case where second member 62B isintegrally molded using a molding die in accordance with theabove-described conventional method, that is, in the case where secondmember 62B is integrally molded using a molding die having an internalspace corresponding to second member 62B and provided with innercircumferential side gate 510 a in the internal space on the innercircumferential side of third internal space 500 that is increased inarea in the circumferential direction, the reason of which will bedescribed as set forth below.

The filler in the resin injected into disc-shaped third internal space500 (corresponding to the shape of main plate 620) is more likely tospread due to the shape of this space. In contrast, the filler in theresin injected into each of fourth internal spaces 610, 650 and 630(corresponding to the shapes of outer blade member 622 b, inner blademember 622 a and intermediate blade member 625, respectively) is morelikely to be oriented in the extending direction of each of fourthinternal spaces 610, 650 and 630 due to the shapes of these spaces. Thisis because third internal space 500 has a shape that allows the resin toflow in various directions, whereas fourth internal spaces 610, 650 and630 each have a shape that causes the resin to flow only in a certaindirection (the direction in which each internal space extends).

By causing the resin to flow only in a certain direction in each offourth internal spaces 610, 650 and 630, a filler is to be oriented withhigh orientation property (alignment property) in each of fourthinternal spaces 610, 650 and 630. Such orientation of the filler acts tostrongly resist radial shrinkage of the resin in third internal space500. This resistance causes a difference in the amount of shrinkage ofmain plate 620 in the radial direction of main plate 620 between aregion where second blade 622 is formed and a region where second blade622 is not formed. This leads to uneven shrinkage of the resin in theradial direction at the time of molding of main plate 620, with theresult that the uniformity of the shape of main plate 620 is decreased.

If the uniformity of the shape of main plate 620 is decreased, fixationof first member 62A and second member 62B using a jig becomes unstableat the time of ultrasonic welding. The same also applies to the casewhere the uniformity of the shape of annular shroud 623 is relativelypoor.

In contrast, in impeller 62 of the present embodiment, second frontsurface 620 a of main plate 620 has: an inner circumferential side gatemark 51 a located on circumference G on the inner circumferential side;and an outer circumferential side gate mark 52 a located oncircumference H close to the outer circumferential side relative toinner circumferential side gate mark 51 a. In other words, the impellerof the present embodiment is molded by injecting a resin containing afibrous filler from each of inner circumferential side gate 510 a andouter circumferential side gate 520 a using a molding die having innercircumferential side gate 510 a provided on the circumference on theinner circumferential side of disc-shaped third internal space 500 andouter circumferential side gate 520 a located on the circumference closeto the outer circumferential side relative to inner circumferential sidegate 510 a.

When a resin is injected from inner circumferential side gate 510 alocated on the circumference on the inner circumferential side of thirdinternal space 500 and from outer circumferential side gate 520 alocated on the circumference close to the outer circumferential siderelative to inner circumferential side gate 510 a, the flow of the resinmoving from outer circumferential side gate 520 a into the space of themolding die exerts an influence upon the flow of the resin moving frominner circumferential side gate 510 a into the space of the molding die.This causes a disturbance in the flow of the resin flowing from innercircumferential side gate 510 a into the space of the molding die.Accordingly, the orientation of the filler in each of fourth internalspaces 610, 650 and 630 can be suppressed as compared with the casewhere a resin is injected only from inner circumferential side gate 510a, so that resistance by the filler oriented in second blade 622 to beformed can be reduced.

Therefore, for the reasons described above, uneven shrinkage of mainplate 620 in the radial direction caused by existence of second blade622 can be suppressed. Consequently, since the uniformity of the shapeof main plate 620 can be improved, first member 62A and second member62B that includes main plate 620 and second blade 622 can besufficiently welded, so that excellent durability and strength can beachieved while stable air-blowing performance can be exhibited.

In main plate 620 of the impeller as described above, innercircumferential side gate mark portion 51 has a plurality of innercircumferential side gate marks 51 a while outer circumferential sidegate mark portion 52 has a plurality of outer circumferential side gatemarks 52 a. In this case, since a resin can be injected in from theplurality of inner circumferential side gates 510 a and the plurality ofouter circumferential side gates 520 a at the time of molding, theuniformity of the shape of second member 62B is further improved.

Furthermore, in the present embodiment, inner circumferential side gatemarks 51 a are located at regular intervals on a correspondingcircumference while outer circumferential side gate marks 52 a arelocated at regular intervals on a corresponding circumference. In thiscase, since the resin can be spread evenly in the circumferentialdirection at the time of molding, the uniformity of the shape of secondmember 62B is further improved.

Furthermore, in the present embodiment, a corresponding one of innercircumferential side gate marks 51 a and a corresponding one of outercircumferential side gate marks 52 a are located on the same straightline extending in the radial direction on the same plane. Consequently,the flow of the resin coming from outer circumferential side gate 520 aexerts a great influence upon the flow of the resin coming from innercircumferential side gate 510 a at the time of molding of second member62B. This causes a great disturbance in the flow of the resin comingfrom inner circumferential side gate 510 a into the space of the moldingdie. Therefore, orientation of the filler in second blade 622 can befurther suppressed, so that uneven shrinkage of main plate 620 in theradial direction caused by existence of second blade 622 can be furthersuppressed.

Furthermore, in the impeller of the present embodiment, first frontsurface 623A of shroud 623 has: an inner circumferential side gate mark31 a located on circumference E on the inner circumferential side; andan outer circumferential side gate mark 32 a located on circumference Fclose to the outer circumferential side relative to innercircumferential side gate mark 31 a. In other words, the impeller of thepresent embodiment is molded by injecting a resin containing a fibrousfiller from each of inner circumferential side gate 310 a and outercircumferential side gate 320 a using a molding die having innercircumferential side gate 310 a provided on the circumference on theinner circumferential side of annular first internal space 300 and outercircumferential side gate 320 a located on the circumference close tothe outer circumferential side relative to inner circumferential sidegate 310 a.

When a resin is injected in from inner circumferential side gate 310 alocated on the circumference on the inner circumferential side of firstinternal space 300 and from outer circumferential side gate 320 alocated on the circumference close to the outer circumferential siderelative to inner circumferential side gate 310 a, the flow of the resincoming from outer circumferential side gate 320 a into the space of themolding die exerts an influence upon the flow of the resin coming frominner circumferential side gate 310 a into the space of the molding die.This causes a disturbance in the flow of the resin flowing from innercircumferential side gate 310 a into the space of the molding die.Accordingly, the orientation of the filler in second internal space 400can be suppressed as compared with the case where a resin is injected inonly from inner circumferential side gate 310 a, so that the resistanceby the filler oriented in first blade 621 to be formed can be reduced.

Therefore, for the reasons as described above, uneven shrinkage ofshroud 623 in the radial direction caused by existence of first blade621 can be suppressed. Consequently, since the uniformity of the shapeof shroud 623 can be improved, second member 62B and first member 62Athat includes shroud 623 and first blade 621 can be sufficiently welded.Accordingly, excellent durability and strength can be achieved whilestable air-blowing performance can be exhibited.

In shroud 623 of the impeller as described above, inner circumferentialside gate mark portion 31 has a plurality of inner circumferential sidegate marks 31 a while outer circumferential side gate mark portion 32has a plurality of outer circumferential side gate marks 32 a. In thiscase, since a resin can be injected in from the plurality of innercircumferential side gates 310 a and the plurality of outercircumferential side gates 320 a at the time of molding, the uniformityof the shape of first member 62A is further improved.

Furthermore, in the present embodiment, inner circumferential side gatemarks 31 a are located at regular intervals on a correspondingcircumference while outer circumferential side gate marks 32 a arelocated at regular intervals on a corresponding circumference. In thiscase, since the resin can be spread evenly in the circumferentialdirection at the time of molding, the homogeneity of first member 62A isimproved.

Furthermore, in the present embodiment, a corresponding one of innercircumferential side gate marks 31 a and a corresponding one of outercircumferential side gate marks 32 a are located on the same straightline extending in the radial direction on the same plane. Consequently,the flow of the resin coming from outer circumferential side gate 320 aexerts a great influence upon the flow of the resin coming from innercircumferential side gate 310 a at the time of molding of first member62A. This causes a greater disturbance in the flow of the resin comingfrom inner circumferential side gate 310 a into the space of the moldingdie. Therefore, the orientation of the filler in first blade 621 can befurther suppressed, so that uneven shrinkage of shroud 30 in the radialdirection caused by existence of first blade 621 can be suppressed.

Seventh Embodiment

The seventh embodiment will be hereinafter described with reference toFIGS. 37 to 39. The present embodiment is different in configuration ofthe second member of the impeller from the sixth embodiment, and otherconfigurations are the same as those in the sixth embodiment.Accordingly, the same description as that in the sixth embodiment willnot be repeated.

(Configuration)

Referring mainly to FIG. 37, second member 62B is different from that inthe sixth embodiment in the point that outer circumferential side gatemarks 52 a forming outer circumferential side gate mark portion 52 eachhave an elliptical shape. It is to be noted that inner circumferentialside gate marks 51 a and outer circumferential side gate marks 52 a inthe sixth embodiment each have a circular shape. This second member 62Bcan be integrally molded as described below.

(Method of Molding Second Member)

Referring mainly to FIGS. 38 and 39, first prepared is a molding diehaving an internal space 200B including: third internal space 500(corresponding to the shape of main plate 620); a plurality of fourthinternal spaces 610, 650 and 630 (corresponding to the shapes of outerblade member 622 b, inner blade member 622 a and intermediate blademember 625, respectively) protruding from third internal space 500; andfifth internal space 700 (corresponding to the shape of boss portion624). Internal space 200B (the space including third internal space 500,fourth internal spaces 610, 650 and 630, and fifth internal space 700)of this molding die is the same as that in the sixth embodiment becauseit has a shape corresponding to the shape of second member 62B to bemolded.

The above-described molding die is further provided with a gate throughwhich a resin is injected into a space having a shape corresponding tothe shape of second member 62B.

In this case, the seventh embodiment is different from the sixthembodiment in the angle of outer circumferential side gate 520 a to theportion corresponding to second front surface 620 a of main plate 620.Specifically, in the sixth embodiment, the ends of inner circumferentialside gate 510 a and outer circumferential side gate 520 a come incontact approximately perpendicularly with the portion corresponding tosecond front surface 620 a of main plate 620. On the other hand, in thepresent embodiment, outer circumferential side gate 520 a comes incontact with the portion corresponding to second front surface 620 a ofmain plate 620 at a slanting angle. This is for the purpose of causingthe resin injected from outer circumferential side gate 520 a to flow inthe circumferential direction in third internal space 500.

Accordingly, outer circumferential side gate 520 a is designed so as tobe arranged at a slanting angle to the plane corresponding to secondfront surface 620 a (approximately 45° in FIG. 39) and arranged at aslanting angle also to the circumferential direction of second frontsurface 620 a (approximately 45° in FIG. 38). In this case, theexpression that outer circumferential side gate 520 a is “arranged at aslanting angle to the plane corresponding to second front surface 620 a”means that outer circumferential side gate 520 a is provided so as tocome in contact with the internal space of second member 62B at aslanting angle when the internal space of second member 62B is seen fromthe direction in which third internal space 500 extends (thecircumferential direction) (FIG. 39). Furthermore, the expression thatouter circumferential side gate 520 a is “arranged at a slanting angleto the circumferential direction of second front surface 620 a” meansthat outer circumferential side gate 520 a is provided so as to come incontact with the space of second member 62B at a slanting angle when theplane corresponding to second front surface 620 a of second member 62Bis seen in top down view (FIG. 38).

Accordingly, when a resin containing a fibrous filler is injected fromouter circumferential side gate 520 a, this resin can flowpreferentially in the circumferential direction on the outercircumferential side of the internal space of the molding die ascompared with the case in the sixth embodiment. Therefore, the filler inthe resin injected from outer circumferential side gate 520 a can beremarkably suppressed from being oriented in fourth internal spaces 610,650 and 630. Furthermore, the filler in the resin injected from innercircumferential side gate 510 a can be more remarkably suppressed frombeing oriented on the outer circumferential side of fourth internalspaces 610, 650 and 630. Since the details of the molding method otherthan the above are the same as those in the sixth embodiment,description thereof will not be repeated.

(Functions and Effects)

Due to its shape, radial shrinkage of third internal space 500 tends tobe greater on the outer circumferential side than on the innercircumferential side. In contrast, in the impeller of the presentembodiment, resistance by the filler is more remarkably suppressed onthe outer circumferential side of second member 62B, so that unevenshrinkage of main plate 620 in the radial direction caused by existenceof second blade 622 can be remarkably suppressed.

Accordingly, the uniformity of the shape of main plate 620 can befurther improved, thereby allowing sufficient welding between firstmember 62A and second member 62B that includes main plate 620 and secondblade 622. Therefore, excellent durability and strength can be achievedwhile stable air-blowing performance can be exhibited.

Although second member 62B has been described in the present embodiment,the same also applies to first member 62A. Specifically, when firstmember 62A is integrally molded, it may be possible to use a molding diethat is designed so as to cause outer circumferential side gate 320 a tocome in contact with the internal space of first member 62A at aslanting angle. In this case, outer circumferential side gate mark 32 aincluded in first member 62A has an elliptical shape.

Eighth Embodiment

The present embodiment is different in configuration of second member62B of the impeller and in specific material of second member 62B fromthe sixth embodiment, and other configurations are the same as those inthe sixth embodiment. Accordingly, the same description as that in thesixth embodiment will not be repeated.

(Configuration)

In the present embodiment, second member 620B is integrally molded usinga resin containing a fibrous filler and a spherical filler.Specifically, second member 620B is integrally molded by injecting aresin containing a fibrous filler from the position corresponding toinner circumferential side gate mark 51 a and by injecting a resincontaining a spherical filler from the position corresponding to outercircumferential side gate mark 52 a.

Accordingly, in second member 62B, a spherical filler is to be containedmore on the outer circumferential side than on the inner circumferentialside while a fibrous filler is to be contained more on the innercircumferential side than on the outer circumferential side.

(Functions and Effects)

As described above, due to its shape, radial shrinkage of third internalspace 500 tends to be greater on the outer circumferential side than onthe inner circumferential side. In contrast, in the impeller of thepresent embodiment, second member 62B is to contain more sphericalfiller and less fibrous filler on the outer circumferential side ascompared with the sixth embodiment. Accordingly, since the resistance bya filler is more remarkably suppressed on the outer circumferential sideof second member 62B, uneven shrinkage of main plate 620 in the radialdirection by existence of second blade 622 can be remarkably suppressed.

Accordingly, the uniformity of the shape of main plate 620 can befurther improved, thereby allowing sufficient welding between firstmember 62A and second member 62B that includes main plate 620 and secondblade 622. Therefore, excellent durability and strength can be achievedwhile stable air-blowing performance can be exhibited.

Although second member 62B has been described in the present embodiment,the same also applies to first member 62A. Specifically, when firstmember 62A is to be integrally molded, a resin containing a fibrousfiller may be injected from the position of inner circumferential sidegate mark 31 a and a resin containing a spherical filler may be injectedfrom the position of outer circumferential side gate mark 32 a. In thiscase, first member 62A is to contain a spherical filler more on theouter circumferential side than on the inner circumferential side and tocontain a fibrous fillers more on the inner circumferential side than onthe outer circumferential side. Consequently, the resistance by thefiller on the outer circumferential side of first member 62A can be moreremarkably suppressed.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the scopeof the present invention being interpreted by the terms of the appendedclaims.

What is claimed is:
 1. An impeller comprising: a main plate formed in adisc shape and having a first plane and a second plane on a sideopposite to said first plane; a plurality of first blades each welded tosaid first plane of said main plate so as to extend from an innercircumferential side to an outer circumferential side of said firstplane and protrude from said first plane; a shroud covering saidplurality of first blades; and a plurality of second blades each formedso as to extend from an inner circumferential side to an outercircumferential side of said second plane and protrude from said secondplane, said main plate and said plurality of second blades beingintegrally molded by a resin containing a fibrous filler, said secondblades each having at least one of a configuration in which each saidsecond blade extends so as to cross a radial direction of said mainplate and a configuration in which each said second blade is separatedby a slit into an inner blade member located on the innercircumferential side and an outer blade member located on the outercircumferential side.
 2. The impeller according to claim 1, wherein atleast a part of each said second blade is formed in a curved line inplan view as seen from a direction orthogonal to said second plane ofsaid main plate.
 3. The impeller according to claim 1, wherein each saidsecond blade has an S-shape in plan view as seen from a directionorthogonal to said second plane of said main plate.
 4. The impelleraccording to claim 1, wherein each said second blade is configured to beseparated by said slit into said inner blade member located on the innercircumferential side and said outer blade member located on the outercircumferential side, and a third blade extending from the innercircumferential side to the outer circumferential side of said secondplane is provided between said outer blade members adjacent to eachother.
 5. The impeller according to claim 1, wherein a positioningprotrusion is provided at an end of each said first blade on a sideopposite to said shroud, a positioning hole is provided in said secondplane of said main plate between said second blades adjacent to eachother, and said protrusion is fitted in said hole.
 6. The impelleraccording to claim 1, wherein a boss portion protruding from said firstplane is provided in a center portion of said main plate, a bearing holepenetrating from said first plane toward said second plane is providedin a center portion of said boss portion, said boss portion is formed soas to be continuously increased in size from an end portion of said bossportion toward said first plane, and a thinned portion is provided insaid boss portion on the second plane side.